When you're apart of an infamous "hacktivist" group like Anonymous, you should always be on the defensive, even when you're on the offensive. Despite being sheathed in a digital cloak of anonymity, there's a host of people gunning for you. Such was the case in March when an unknown party infected a denial-of-service (DDoS) program called Sloworis which was known to be used by the Anonymous crew when taking down corporate websites.
The program was infected with the Zeus Trojan, a malware designed to steal banking and credit card information from the computer it infects. So each time an Anonymous user fired up Sloworis to perform a DDoS on one of the group's many targets, they were unknowingly helping another hacker group steal their personal information. Live by the hack, die by the hack.