SpyEye Trojan changes code to avoid detection and widens global reach

Banking security firm Trusteer has warned that the infamous information-stealing SpyEye Trojan has expanded its global reach to target even more countries, while adapting its code to circumvent banks' transaction monitoring systems.

Trusteer chief executive Mickey Boodaei explained in an updated blog post that the majority of botnet activity is aimed at UK and US computers, but that countries including Japan, China and Russia, among numerous others, have been added to the hitlist in the past three months.

SpyEye is often described as a cheaper alternative to ZeuS, but Boodaei explained that it appears to differ in one important way, in that it incorporates new code designed to bypass traditional filters.

"Transaction monitoring systems analyse various aspects of the customer's session with the bank in order to detect abnormal behaviour that may be attributed to malware activity," he said.

"SpyEye developers appear to have figured how these defences operate and are now constantly trying to ensure their code activity flies under the radar of these detection systems."

The Trojan's writers also appear to follow Agile software development practices, meaning that the malware can be updated very quickly in response to the most recent attempts to block it.

"At certain times, we have even seen two new versions of the malware released every week. It's important to note that there is a large difference between a new version and a simple variant of financial malware," said Boodaei.

"A new version means that the program code itself has been modified, while a new variant is just new packing around the same code."

SpyEye has been a constant thorn in the side of the online banking industry since its appearance in late 2009, but efforts have been stepped up to check its progress.

In June, Virgin Media said it had been working with the Serious Organised Crime Agency to warn customers about the Trojan, following up the ISP's work in highlighting the risk from the Zeus Trojan in 2010.