# Anomaly Detection in Blockchain: A Systematic Review of Trends, Challenges, and Future Directions
## 3 Results
### Analysis of the Collaboration Network Among Countries  
Figure 3 illustrates the global collaboration network among countries involved in blockchain anomaly detection research, comprising 77 countries connected by 254 collaborative links.  
With a network density of 0.0868, this structure reveals a relatively sparse yet highly concentrated research landscape. A low density suggests that, while strong collaborative clusters exist, overall global cooperation is not yet fully integrated. This implies potential challenges for efficient knowledge diffusion and the establishment of unified research priorities across the field.  
China dominates the field with 137 publications (34.42% of total), demonstrating significant strategic investment in blockchain security research. The United States (63 publications, 15.83%) and India (51 publications, 12.81%) form the second tier, collectively accounting for nearly two-thirds of global output. Saudi Arabia emerges as a regional leader with 34 publications (8.54%), surpassing several technologically advanced nations.  
The analysis of the research ecosystem reveals a landscape characterized by four distinct geographical clusters:  
1. Asian cluster: Dominated by China (34.42%), which reflects the country's national blockchain development strategy and centralized research funding mechanisms. South Korea (6.03%) and Taiwan (4.77%) demonstrate strong technical capabilities, particularly in cryptographic implementations. India's (12.81%) growth in this area correlates with its Digital India initiative and the increasing adoption of cryptocurrency [48].  
Figure 3: The collaboration network among countries.  
2. North American cluster: Led by USA (15.83%) researchers and institutions, who are pioneers in developing advanced detection methods, particularly using graph neural networks. Canada (5.28%) also contributes to this cluster.  
3. Middle Eastern cluster: Saudi Arabia (8.54%) leads with its NEOM smart city project and $6.4 billion blockchain investment plan [49]. UAE (2.01%) and Qatar (1.76%) are also emerging as key players with expertise in financial blockchain applications.  
4. European cluster: This cluster presents a more fragmented landscape, but demonstrates high-impact contributions from countries such as England (4.77%), Italy (3.02%), Switzerland (2.51%), and Germany (1.76%). Several collaborative projects in Europe focus on blockchain anomaly detection, bringing together expertise from academia, industry, and international organizations to enhance blockchain security. Notable initiatives include the MSCA Digital Finance project, the anomaly and fraud detection in blockchain networks project by Bern University [50], the project to prevent the criminal use of blockchain technology [51], and the Ontochain initiative [52], all of which address key challenges in fraud detection, security, and innovation within blockchain.  
The long-tail distribution includes 58 countries with 5 or fewer publications, indicating growing global interest.  
This geographical analysis underscores the critical need for standardized international frameworks to address blockchain security challenges, particularly given the technical disparities between leading and emerging research nations. The concentration of research capabilities in specific regions may create asymmetries in global blockchain governance frameworks.