Abstract
JavaScript based attacks have been reported as the top Internet security threats in recent years. Since most of the Internet users rely on anti-virus software to protect themselves from malicious JavaScript code, attackers exploit JavaScript obfuscation techniques to evade the detection of anti-virus software. To better understand the obfuscation techniques adopted by malicious JavaScript code, we conduct a measurement study. We first categorize observed JavaScript obfuscation techniques. Then we conduct a statistic analysis on the usage of different categories of obfuscation techniques in real-world malicious JavaScript samples. We also study the detection effectiveness of 20 most popular anti-virus software against obfuscation techniques. Based on the results, we analyze the cause of the popularity of obfuscation in malicious JavaScript code; the reason behind the choice of obfuscation techniques and the difference between benign obfuscation and malicious obfuscation. Moreover, we also provide suggestions for designing effective obfuscation detection approaches in future.