The virus, dubbed APStrojan.qa, emerged on 25 January and is the most active in a string of similar viruses affecting AOL users that have been identified over the past year, according to antivirus software vendor McAfee. In the past 30 days reports of the virus have increased 100 per cent, said April Goostree, a virus research manager at McAfee.
It wasn't clear exactly how many users have been affected, but the number is "significant," Goostree said. The virus has been rated a medium risk for AOL users, and low to medium risk for corporate users.
A trojan virus is a malicious program that arrives disguised as a harmless application but in fact carries a nasty payload. The AOL trojan takes the form of an attachment named "mine.zip" and spreads itself in an e-mail bearing the subject line "hey you." Text in the body of the message suggests that the attachment contains scanned images, McAfee.com said in a statement.
The virus tries to steal the account numbers and passwords of AOL users and, if successful, will e-mail them back to the author of the virus. This could give the hacker access to user's email and other personal information.
When a user logs onto the AOL service, the virus will also try to e-mail itself to all of the contacts listed in that member's Buddy List. That means users who are not AOL members can also receive the virus. Those non-AOL users are not at risk of having passwords stolen, but the virus will slow down the performance of any PC it infects, Goostree said.
This ability of the virus to e-mail itself to other users occurs only with version 4.0 of AOL's software. Improvements to versions 5.0 and 6.0 prevent the virus from replicating itself, although it can still steal passwords from users of those versions. In addition, when a user of AOL version 6.0 is infected, the virus creates a pop-up message urging the user to switch back to version 4.0 of the software, Goostree said.
AOL 4.0 users constitute a "distinct minority" of members, with most using versions 5.0 or 6.0, said AOL spokesman Andrew Weinstein.
AOL has provided links on its Web site to information about the virus, as well as to a free "one click fix" provided by McAfee.com which is available at http://aol.mcafee.com. However, the company played down the significance of the virus and said it hasn't felt the need to send a warning to its members via e-mail.
"Obviously we can't speak for McAfee, but we haven't seen a significant increase in the number of people affected," Weinstein said.