Symbian worm Yxes: towards mobile botnets?

In 2009, a new Symbian malware named SymbOS/Yxes was detected and quickly hit the headlines as one of the first malware for Symbian OS 9 and above all as the foretaste of a mobile botnet. Yet, detailed analysis of the malware were still missing. This paper addresses this issue and details how the malware silently connects to the Internet, installs new malware or spreads to other victims. Each of these points are illustrated with commented assembly code taken from the malware or re-generated Symbian API calls. Besides those implementation aspects, the paper also provides a global overview of Yxes’s behaviour. It explains how malicious remote servers participate in the configuration and propagation of the malware, including Yxes’s similarities with a botnet. It also tries to shed light on some incomplete or misleading statements in prior press articles. Those statements are corrected, based on the reverse engineering evidence previously. Finally, the paper concludes on Yxes’s importance and the lack of security on mobile phones. It also indicates several aspects future work should focus on such as communication decryption, tools to analyze embedded malware or cybercriminals motivations.