Ismuhadi’s Equation: A Forensic Tool for Detecting Tax Avoidance and Underground Economic Activity in Indonesia

1. Introduction: The Landscape of Tax Evasion and the Role of Forensic Accounting in Indonesia

The persistent challenge of tax evasion and the significant scale of underground economic activity in Indonesia present ongoing obstacles to the nation’s fiscal health and economic stability. Estimates suggest that the shadow economy constitutes a substantial portion of Indonesia’s Gross Domestic Product (GDP), indicating a considerable loss of potential tax revenue for the government. This hidden economic activity not only diminishes the funds available for public services and development but also creates an uneven playing field for legitimate businesses that adhere to tax regulations.

The methods employed to evade taxes are continuously evolving, encompassing increasingly sophisticated schemes. These tactics extend beyond simple underreporting of income to include intricate financial maneuvers such as transfer pricing manipulation, where the pricing of transactions between related entities is used to shift profits to lower-tax jurisdictions, and the establishment of shell companies in tax havens to obscure beneficial ownership and financial flows. The complexity of these schemes necessitates advanced analytical tools and techniques to effectively identify and address them.

In response to these challenges, forensic accounting has emerged as a crucial discipline in Indonesia, blending accounting expertise with investigative skills to detect financial discrepancies and fraudulent activities, particularly in the context of tax compliance. This specialized field plays an increasingly vital role in uncovering financial misconduct and ensuring the integrity of the tax system.

Within this evolving landscape, Ismuhadi’s Equation, also known as the Tax Accounting Equation (TAE), represents an innovative forensic tool developed specifically within the Indonesian tax context. Created by Indonesian tax expert Dr. Joko Ismuhadi Soewarsono, this equation offers a unique approach to analyzing financial data with the aim of detecting potential tax avoidance and uncovering underground economic activity (UEA). Its development signals a proactive effort to address the specific challenges of tax enforcement and compliance within the Indonesian economic and regulatory environment.

2. Deconstructing Ismuhadi’s Equation (TAE): A Forensic Accounting Innovation

At the foundation of financial accounting lies the fundamental Basic Accounting Equation (BAE): Assets = Liabilities + Equity. This equation represents the balance between a company’s resources (assets) and its obligations to external parties (liabilities) and its owners (equity). Expanding upon this is the Expanded Accounting Equation (EAE): Assets = Liabilities + Equity + (Revenues – Expenses – Dividends). The EAE provides a more detailed view of how a company’s operational activities, reflected in its revenues and expenses, and its distributions to owners through dividends, impact its equity.

Dr. Joko Ismuhadi Soewarsono derived Ismuhadi’s Equation, also referred to in some sources as the Mathematical Accounting Equation (MAE) , from these fundamental principles specifically for the purpose of tax analysis. The equation is expressed in two primary forms:

• Revenue – Expenses = Assets – Liabilities
• Revenue = Expenses + Assets – Liabilities

The rationale behind this specific rearrangement of the basic accounting equation centers on establishing a direct link between a company’s profitability, as depicted in its income statement (Revenue minus Expenses), and its net worth, as represented in its balance sheet (Assets minus Liabilities). One formulation isolates revenue, suggesting that a company’s income should logically correlate with its expenses, asset accumulation, and liability management. This approach allows for the establishment of an expected level of revenue based on the other financial statement components, making significant deviations more conspicuous.

The equation implicitly operates on the premise that legitimate business activity should result in a logical and consistent flow between a company’s profitability and its net worth. For instance, increased revenue should ideally lead to an increase in assets or a decrease in liabilities. Deviations from this expected relationship can serve as potential indicators of tax evasion or other financial irregularities.

Furthermore, the TAE can be utilized for the early detection of potentially misleading accounting practices often employed to avoid tax obligations. One such practice involves recording revenues as liabilities and expenses as assets, frequently through the use of clearing accounts, which are temporary accounts intended to have a zero balance at the end of an accounting period. By highlighting unusual inverse relationships between revenue and liabilities, or expenses and assets, the TAE can act as a red flag, prompting tax authorities to conduct more in-depth investigations into these transactions.

3. Dr. Joko Ismuhadi Soewarsono: The Architect of the Tax Accounting Equation

Dr. Joko Ismuhadi Soewarsono, the developer of the Tax Accounting Equation, brings a wealth of both academic rigor and practical experience to the field of Indonesian taxation. He is currently a PhD student specializing in accounting at Padjadjaran University in Bandung, Indonesia. His academic pursuits are significantly enhanced by his extensive professional career as a Tax Auditor at the Directorate Generale Tax in Jakarta, Indonesia, a position he has held since August 2008 and within which he currently serves in a supervisory role. This dual role as an academic and a tax auditor provides him with a unique perspective, blending theoretical knowledge with firsthand insights into the complexities and challenges of tax administration and enforcement within the Indonesian context.

Dr. Soewarsono’s academic contributions and research interests are broad, encompassing areas critical to understanding and combating tax evasion. These include tax planning, financial engineering, scheme transactions, corporate finance, valuation, and, notably, the application of mathematical approaches to detect tax evasion, as well as the analysis of digital services taxes. His interdisciplinary approach is further underscored by his attainment of a doctorate in tax criminal law, alongside his ongoing doctoral candidacy in tax accounting. This background suggests a deep understanding of not only the financial and accounting aspects of tax evasion but also its legal and criminal dimensions.

His commitment to the field is evident in his authorship of “Tindak Pidana Korporasi. Analisis Manipulasi Pajak dengan Perbuatan Pencucian Uang” (Corporate Crime. Analysis of Tax Manipulation with Money Laundering). This publication indicates a research focus that extends beyond mere tax avoidance to address the more severe issue of criminal tax manipulation and its frequent connection to money laundering activities, highlighting his understanding of the motivations and far-reaching consequences of tax evasion.

Dr. Soewarsono actively engages in academic discussions through platforms such as ResearchGate, sharing his research and insights with the scholarly community. He is also affiliated with prominent academic and professional organizations, including the Association of Tax Centers and Tax Academics of All Indonesia (Pertapsi) and the Association of Indonesian Legal Experts (Perkahi). While his primary focus in recent discussions and publications has been on the Tax Accounting Equation, his ResearchGate profile also lists publications such as conference papers on intellectual property rights and legal protection for default debtors in online loan agreements. These diverse research interests demonstrate a wide-ranging expertise in financial and legal matters relevant to taxation , lending further credibility to his work on the TAE.

4. Unmasking the Underground Economy: How Ismuhadi’s Equation Serves as a Detection Tool

The underground economy in Indonesia represents a significant portion of the nation’s economic activity, characterized by transactions that evade official recording and government oversight. This hidden realm encompasses a wide range of activities, from illegal operations like drug trafficking and smuggling to unreported income from legitimate businesses seeking to avoid tax obligations. A common thread in many underground economic activities is the prevalence of cash transactions, which are inherently more difficult to trace than electronic payments, making it easier to conceal income and evade regulatory scrutiny. Industries dealing with a high volume of cash, such as food distribution, cigarette sales, and the drug industry, are particularly susceptible to underground economic activities due to the ease with which cash can be exchanged and the difficulty in tracing its origin.

Ismuhadi’s Equation offers a valuable tool for tax authorities to detect potential underground economic activity, particularly within these cash-intensive sectors, by identifying anomalies in financial reporting that might indicate hidden income or inflated expenses. The equation’s structure allows for the analysis of the relationships between key financial statement components to uncover suspicious patterns.

One key application lies in identifying unusual liability levels. In legitimate businesses, an increase in revenue typically correlates with a decrease in liabilities as debts are paid off. However, in cash-intensive businesses involved in the underground economy, a different pattern might emerge. If a business reports significantly increasing liabilities despite also reporting high revenue, this could indicate an attempt to conceal income by disguising it as debt. Ismuhadi’s Equation, by focusing on the interplay between revenue and liabilities, can effectively flag such discrepancies that deviate from expected financial behavior.

Furthermore, the equation can aid in detecting discrepancies between expected and reported revenue. By analyzing the relationship between a company’s assets, liabilities, and expenses, the TAE can establish an expected level of revenue required to sustain its operations and financial position. If the reported revenue significantly deviates from this expectation, particularly in cash-intensive industries where income can be easily hidden, it could signal the presence of unreported cash transactions, a hallmark of underground economic activity.

Ismuhadi’s Equation also provides tax authorities with a quantitative method to screen financial data and prioritize audits for businesses with suspicious financial patterns, especially those in high-risk, cash-intensive sectors. This targeted approach allows for a more efficient allocation of limited audit resources, focusing on businesses where the risk of unreported income is higher. The equation acts as an early warning system, helping to identify potential tax evaders before their activities become deeply entrenched or difficult to trace.

Unlike traditional audit methods that might focus on specific income or expense items, Ismuhadi’s Equation offers a holistic view of financial activities by examining the interplay between all key financial statement components. This broader perspective can reveal inconsistencies and manipulations that might be missed through conventional analysis, where individual accounts might appear reasonable in isolation.

The inherent nature of cash-intensive transactions makes businesses in these sectors more vulnerable to involvement in the underground economy. Cash transactions are difficult to trace, leaving no direct audit trail and facilitating the concealment of illicit funds. Illegitimate cash can be easily commingled with legitimate cash revenue, making it challenging to distinguish between the two. Moreover, cash payments can facilitate off-the-books transactions that are not officially recorded, allowing businesses to evade taxes and operate outside regulatory oversight. By applying Ismuhadi’s Equation to the financial data of distributors in sectors like food, cigarettes, and drugs, Indonesian tax authorities can gain valuable insights into potential underground economic activities fueled by these cash-intensive transactions.

5. The Indonesian Tax Authority’s Arsenal: Utilizing Forensic Accounting Tools like Ismuhadi’s Equation

The Directorate General of Taxes (DJP) in Indonesia bears the crucial responsibility of collecting state revenue and combating tax evasion, which poses a significant threat to the nation’s economic well-being. To fulfill this mandate, the DJP is continuously seeking and adopting advanced tools and techniques to enhance its audit capabilities and identify non-compliant taxpayers. Ismuhadi’s Equation holds the potential to be a valuable addition to the DJP’s arsenal of forensic accounting tools.

The DJP could potentially integrate Ismuhadi’s Equation into its existing audit methodologies as an initial screening mechanism. By applying the equation to the financial statements of a large number of taxpayers, the DJP could identify those exhibiting financial patterns that deviate significantly from expected norms. This would allow the tax authority to prioritize its audit efforts, focusing its limited resources on taxpayers who present a higher risk of tax evasion or involvement in the underground economy. Such a targeted approach would likely increase the efficiency and effectiveness of the DJP’s audit processes.

Recognizing the increasing importance of technology in combating financial crime, the DJP has been actively adopting data analytics and digital systems, including the implementation of the CoreTax Administration System (Coretax). Coretax aims to enhance transparency by integrating taxpayer data with information from various third-party sources and providing real-time access to financial transactions. Ismuhadi’s Equation could potentially be integrated into such digital platforms, allowing for the automated analysis of financial data and the generation of alerts for potentially suspicious activities.

Beyond Ismuhadi’s Equation, the DJP also utilizes a range of other forensic accounting techniques to combat tax evasion. Digital forensics plays a crucial role in processing and analyzing electronic data to uncover hidden transactions and manipulations. Data mining techniques are employed to sift through vast amounts of financial data to identify patterns indicative of tax fraud, such as inconsistencies in VAT reporting. These diverse tools and techniques demonstrate the DJP’s commitment to a multi-faceted approach in its efforts to ensure tax compliance. Ismuhadi’s Equation, with its unique focus on the relationship between profitability and net worth, could serve as a valuable complement to these existing methods.

6. Illuminating Discrepancies: Case Studies and Practical Applications of Ismuhadi’s Equation

While publicly available, detailed case studies specifically naming Indonesian companies and explicitly using Ismuhadi’s Equation might be limited, the underlying principles and potential applications of the equation in uncovering discrepancies indicative of tax avoidance are evident from the available information. The equation’s creator, Dr. Joko Ismuhadi Soewarsono, has highlighted its use in analyzing financial statements to detect early signs of tax evasion.

Consider a hypothetical scenario involving a cash-intensive food distributor. This business reports a significant increase in revenue, ostensibly due to a surge in demand. However, a closer look at its balance sheet reveals a simultaneous and substantial increase in short-term liabilities, such as accounts payable, without a corresponding rise in inventory levels or fixed assets. Applying Ismuhadi’s Equation in the form of Revenue = Expenses + Assets – Liabilities might reveal that the reported revenue figure is not logically consistent with the changes in the company’s asset and liability positions. This inconsistency could suggest that the actual cash inflows from the increased revenue are being underreported and potentially disguised as increased payables to reduce the apparent profitability and, consequently, the tax liability.

Another hypothetical scenario could involve a cigarette distributor that engages in transactions with related parties located overseas. The distributor reports high revenue from exports but also shows exceptionally high liabilities to these related foreign entities. Utilizing Ismuhadi’s Equation in the form of Revenue – Expenses = Assets – Liabilities might highlight a significant disparity between the reported profitability (Revenue – Expenses) and the net assets (Assets – Liabilities) of the company. This could be a potential indicator of profit shifting, where profits generated in Indonesia are being transferred to related parties in lower-tax jurisdictions through inflated liabilities, thereby reducing the taxable income in Indonesia.

Dr. Soewarsono himself has provided a case study involving the Crude Palm Oil (CPO) industry in Indonesia. His research indicated that some companies in this sector were potentially recording income as liabilities and expenses as assets to avoid both Corporate Income Tax (PPh) and Value Added Tax (VAT). This unconventional accounting practice, when analyzed through the lens of the Tax Accounting Equation, resulted in a consistent pattern of reported corporate income tax and monthly value-added tax overpayments, raising red flags for tax authorities. This real-world example underscores the practical utility of the TAE in identifying specific tax avoidance schemes within a key Indonesian industry.

Furthermore, a YouTube discussion highlighted the potential application of Ismuhadi’s Equation in the context of a mining company. In this example, the company reported high revenue from exports but also significant liabilities to related parties. This discrepancy, identified through the relationship analysis inherent in Ismuhadi’s Equation, could suggest transfer pricing manipulation aimed at reducing the company’s tax burden in Indonesia.

These examples, both hypothetical and based on reported instances, illustrate the potential of Ismuhadi’s Equation to illuminate discrepancies in financial statements that might otherwise go unnoticed, providing tax authorities with valuable leads for further investigation and potential detection of tax avoidance and underground economic activity.

7. Navigating the Nuances: Limitations and Criticisms of Ismuhadi’s Equation

While Ismuhadi’s Equation presents a promising tool for detecting tax avoidance and underground economic activity, it is important to acknowledge its limitations and potential criticisms. Like any analytical method relying on financial data, the equation’s effectiveness is inherently tied to the accuracy and completeness of the financial statements provided by taxpayers. If a company intentionally falsifies its accounting records, a practice often referred to as “cooking the books,” the TAE might fail to detect the underlying manipulation, as it would be analyzing flawed input data.

Furthermore, Ismuhadi’s Equation primarily focuses on quantitative data derived from the financial statements. While these numbers provide a valuable snapshot of a company’s financial position and performance, they do not always capture the full picture of its operations and tax behavior. Qualitative factors, such as a company’s specific business model, its management practices, and the unique nuances of the industry in which it operates, can also significantly influence its tax liability. These qualitative aspects might not be readily apparent from the equation’s output alone, necessitating a more comprehensive analysis that combines quantitative findings with qualitative insights.

The interpretation of the results generated by Ismuhadi’s Equation requires a significant level of expertise in both tax accounting principles and financial analysis. It is not a simple formula that can be applied and understood without professional judgment. Analysts need a deep understanding of Indonesian tax regulations and financial reporting standards to correctly interpret any discrepancies flagged by the equation and to determine whether these discrepancies genuinely indicate tax evasion or can be attributed to legitimate business factors.

It is also crucial to recognize that Ismuhadi’s Equation is not a foolproof solution or a “silver bullet” for combating tax evasion. While it offers a valuable tool for early detection and risk assessment, it should be used as part of a broader, multi-pronged approach. This comprehensive strategy should also include robust tax regulations, strong enforcement mechanisms, and efforts to foster a culture of tax compliance among businesses and individuals.

Beyond the specific limitations of Ismuhadi’s Equation, the broader concept of using modified accounting equations for fraud detection also has its nuances. While the modified equation Revenue = Expenses + Assets – Liabilities can offer a valuable perspective in fraud detection by shifting the analytical focus, it too relies on the integrity of the reported data. Additionally, in its current formulation, Ismuhadi’s Equation might not directly address highly complex tax avoidance strategies employed by multinational corporations, such as sophisticated transfer pricing schemes or the intricate financial flows within cash pooling mechanisms, without further refinement or integration with other specialized analytical techniques.

8. Beyond the Equation: A Broader Look at Forensic Accounting Techniques in Indonesia’s Fight Against Tax Evasion

While Ismuhadi’s Equation offers a novel approach to detecting tax avoidance, the Indonesian tax authority also employs a range of other forensic accounting techniques to combat this issue.

Digital forensics has become increasingly critical in today’s digital economy. This involves the systematic process of collecting, processing, analyzing, and reporting on electronic data that can be used as evidence in tax-related investigations. Techniques such as data recovery, network analysis, and malware analysis fall under this domain, allowing tax authorities to uncover hidden digital trails of financial transactions and communications that may be relevant to tax evasion.

Data mining and analytics play a significant role in sifting through the vast amounts of financial data available to tax authorities. By applying statistical techniques and specialized software, tax authorities can identify patterns, anomalies, and correlations that might indicate fraudulent activities, such as inconsistencies in reported income or deductions, or unusual transaction patterns in VAT reports. Techniques like statistical sampling, Benford’s Law analysis (which examines the frequency distribution of digits in financial data), and trend analysis over time are valuable tools in this area.

Investigative auditing remains a fundamental technique in forensic accounting. This involves utilizing specialized investigative skills to conduct in-depth examinations of financial discrepancies and potential fraud. Such investigations often include tracing the flow of funds, conducting surveillance (where legally permissible), and interviewing individuals who may have knowledge relevant to the case.

The use of Generalized Audit Software (GAS) enhances the efficiency and effectiveness of audits. GAS allows auditors to automate many data analysis tasks, enabling them to quickly examine large volumes of financial data, identify irregularities, and perform tests that would be impractical to do manually.

Whistleblowing systems provide a crucial avenue for uncovering potential tax evasion and other financial misconduct. These systems allow individuals within or outside an organization to anonymously report suspected illegal or unethical activities, providing tax authorities with valuable leads that can trigger more focused investigations.

Finally, fraud risk assessment is a proactive approach that aims to prevent tax evasion before it occurs. By identifying and evaluating potential fraud risks within organizations and the tax system as a whole, authorities can develop and implement preventive and detective controls to mitigate these risks.

9. The Shadowy Realm: Understanding the Underground Economy in Indonesia

The underground economy in Indonesia is a pervasive phenomenon, estimated to constitute a significant portion of the nation’s overall economic activity. Estimates from various sources suggest that this hidden sector accounts for anywhere between approximately 17% and over 20% of the country’s GDP in recent years , with some even higher estimations around 30-40%. This substantial scale underscores the significant challenge it poses to tax authorities and the overall economic health of the nation.

The underground economy in Indonesia encompasses a wide array of activities, both legal and illegal, that are intentionally concealed from official records. This includes criminal activities such as drug trafficking and the smuggling of goods, as well as the unreported income from otherwise legitimate businesses and individuals seeking to evade tax obligations. The informal economy, comprising unregistered businesses and transactions, also forms a significant part of this hidden sector.

The existence of a large underground economy has several detrimental impacts on Indonesia. Most notably, it leads to significant losses in tax revenue for the government, reducing the funds available for essential public services and infrastructure development. Furthermore, it distorts official economic statistics, such as GDP calculations, making it difficult for policymakers to accurately assess the true state of the economy and make informed decisions. The reduced tax base can also lead to higher tax burdens on compliant businesses and individuals, creating an unfair economic environment.

Certain sectors within Indonesia have been identified as being particularly susceptible to underground economic activity. These include agriculture and fisheries, transportation and warehousing, and information and communication. Additionally, cash-intensive industries like food distribution, cigarette sales, and the drug industry are inherently at higher risk due to the ease of concealing cash transactions.

Measuring the true size and scope of the underground economy is a significant challenge due to the inherent secrecy of these activities and the lack of a universally agreed-upon definition. Participants in the underground economy actively seek to conceal their identities and transactions, making direct measurement difficult. This difficulty in quantification underscores the importance of indirect detection methods, such as Ismuhadi’s Equation, that can identify potential indicators of hidden economic activity.

The Indonesian government has increasingly recognized the need to address the underground economy to bolster tax revenue and ensure a fairer economic system. Initiatives are underway to study this sector, identify new potential revenue streams, and explore strategies for bringing informal businesses into the formal economy. However, such efforts also carry potential risks, such as inadvertently legitimizing illicit activities or exacerbating existing issues like corruption.

10. Recent Developments and Future Trajectory of Ismuhadi’s Equation in the Indonesian Tax System

Recent developments indicate a growing recognition and discussion surrounding Ismuhadi’s Equation within the Indonesian tax and accounting communities. Public discussions on platforms like YouTube have highlighted the equation’s potential to modernize traditional accounting methodologies and enhance both tax detection and planning capabilities in Indonesia. This public discourse suggests a growing awareness and interest in the tool’s potential contribution to tax administration.

Furthermore, recent news articles in May 2025 on taxjusticenews.com have featured “Persamaan Ismuhadi” (Ismuhadi’s Equation) as an Indonesian innovation in forensic tax analysis. These articles emphasize the equation’s role as a forensic accounting tool specifically tailored for Indonesian tax analysis, highlighting its utility in scrutinizing financial data to uncover evidence of past tax evasion or financial manipulation. This media attention signifies the ongoing relevance and potential impact of Ismuhadi’s Equation within the Indonesian tax landscape.

The Tax Accounting Equation holds significant potential for influencing tax policy innovation and administration in Indonesia. By offering a data-driven approach to identifying potential tax risks and providing valuable insights into the patterns and methods used by tax evaders, the TAE could inform the development of more targeted and effective tax policies and enforcement mechanisms. Given Dr. Soewarsono’s background and experience within the Directorate General of Taxes, his research and the TAE could be considered for wider adoption or to influence internal practices within the tax authority.

Dr. Soewarsono’s ongoing PhD research and academic engagement further contribute to the academic discourse on taxation and financial governance in Indonesia. The TAE serves as a novel analytical model within this research, potentially stimulating further academic inquiry into the areas of forensic tax accounting and the application of quantitative methods in tax analysis.

Looking ahead, the future trajectory of Ismuhadi’s Equation in the Indonesian tax system could involve its integration with other forensic accounting techniques and data analytics tools. Combining the unique insights offered by the TAE with the power of digital forensics, data mining, and advanced audit software could lead to the development of more comprehensive and effective tax evasion detection systems.

11. Conclusion: The Significance of Ismuhadi’s Equation in Indonesia’s Anti-Tax Evasion Efforts

Ismuhadi’s Equation, or the Tax Accounting Equation (TAE), developed by Dr. Joko Ismuhadi Soewarsono, represents a significant innovation in the field of forensic accounting within the Indonesian tax context. By rearranging the fundamental accounting equation, the TAE provides a targeted approach to detect potential tax avoidance and uncover underground economic activity, particularly in cash-intensive industries. Its core principle lies in analyzing the relationship between a company’s profitability and its net worth to identify discrepancies that might indicate hidden income or manipulated expenses.

The TAE offers value as a targeted forensic tool, allowing tax authorities to screen financial data and prioritize audits for businesses exhibiting suspicious patterns. Its holistic view of financial activities can reveal inconsistencies that might be missed by traditional methods. Specifically, the equation can help identify unusual liability levels in cash-intensive businesses and detect deviations between expected and reported revenue, both common indicators of underground economic activity.

However, it is crucial to acknowledge the limitations of Ismuhadi’s Equation. Its effectiveness depends on the accuracy of financial statements and primarily focuses on quantitative data. The interpretation of its results requires expertise, and it should be viewed as one component of a broader strategy to combat tax evasion.

Indonesian tax authorities (DJP) should explore the potential for wider adoption and integration of Ismuhadi’s Equation into their audit and risk assessment processes. Given the DJP’s increasing embrace of technology through initiatives like the Coretax system, there is an opportunity to incorporate the TAE into these digital frameworks for automated analysis and early detection of potential tax evasion.

Further academic research is also warranted to empirically validate the effectiveness of the TAE across various sectors of the Indonesian economy and to explore potential enhancements or adaptations that could address its limitations or extend its applicability to more complex tax avoidance schemes, such as those involving multinational corporations and intricate financial instruments.

In conclusion, Ismuhadi’s Equation holds considerable promise as a valuable tool in Indonesia’s ongoing efforts to foster a more transparent, equitable, and efficient tax system by providing a novel and targeted method for detecting tax avoidance and uncovering the hidden activities of the underground economy.