The Zeus/ZBOT Trojan is no newcomer to the malware scene, but that hardly means it does not have any new tricks up its sleeve.
According to Trend Micro, researchers have discovered a new version of the ZBOT that is self-propagating. This is a new trick for ZBOT, which typically spreads through drive-by downloads that occur when users visit sites compromised to host exploit kits serving the malware.
“This particular ZBOT variant arrives through a malicious PDF file disguised as a sales invoice document,” blogged Abigail Pichel of Trend Micro.
If the user opens the file with Adobe Reader, it triggers an exploit that causes a pop-up window appear.
“While this is going on, the malicious ZBOT variant – WORM_ZBOT.GJ – is dropped onto the system and run. It is here that several differences start to appear,” Pichel explained. “First of all, WORM_ZBOT.GJ has an autoupdate routine: it can download and run an updated copy of itself. Secondly, however, it can spread onto other systems via removable drives, like USB thumb drives. It does thus by searching for removable drives and then creating a hidden folder with a copy of itself inside this folder, and a shortcut pointing to the hidden ZBOT copy.”
In February, Trend Micro observed an increase in ZBOT samples. The surge in new infection attempts continued through at least May 7. The new propagation technique is unusual for ZBOT, Pichel noted, and could mean an increase in ZBOT infections moving forward.
“This unusual behavior, however, is in line with our2013 predictions, which noted that we believed that older threats would continue to be seen in 2013, although they would have refinements to make them more effective. In the past, some ZBOT variants have used unusual means – like file infectors – to spread as well,” she blogged.