A trojan, or trojan horse, is a program containing malicious code which is hidden within otherwise harmless programming. When it enters into a computer, it can be triggered to corrupt other data. If widely distributed, it is considered to be a virus.
McAfee.com explained that the most virulent strain of the AOL trojan, "APStrojan.qa," spreads through e-mail, often carrying the message “hey you” and installs itself on users’ systems, while attempting to steal AOL version 4.0 and 5.0 user account names and passwords, and forward them. It then attempts to replicate itself to active AOL screen names listed in the infected user’s "Buddy List." This trojan was designed to provide unauthorised access to victims’ AOL user accounts, including e-mail.
While variants of the APStrojan have been circulating for nearly a year, McAfee.com has recently noticed a significant increase in infected computers by users who are scanning their PCs at the McAfee.com site. There are roughly 30 variations of the AOL password-stealing trojan, but APStrojan.qa is replicating at a far greater rate than other similar trojans due to its mass-mailing properties.
McAfee.com has been working with AOL to help inform AOL’s members about this issue. Today, McAfee.com posted a free scan and also provides a "one-click" fix for AOL users to remove this trojan at http://aol.mcafee.com.