A security firm has warned AOL users of the rapid spread of a Trojan horse program which can steal their passwords.

Rates of infection among AOL from variants of a piece malicious code, called APStrojan.qa, have doubled in the last month, according to antivirus firm McAfee.com, the consumer arm of Network Associates. It rates the problem as "medium risk".

The Trojan is almost a year old but has recently been developed in order to target AOL communities.

However AOL itself has denied that its users are been significantly affected by the Trojan, which it describes as a "non-issue".

APStrojan.qa is a password stealer and Internet worm written in Visual Basic 5; it has been modified by crackers to target AOL users.

The Trojan commonly comes as an attachment, called mine.zip, accompanying an e-mail entitled 'Hey You'. If opened, the malicious code attempts to steal victims' AOL account names and passwords. It will also attempt to send itself to a users' 'buddylist' if they are logged onto AOL.

Victims are likely to be alerted to the virus only when they have difficulty shutting down their computers.

Andrew Weinstein, a spokesman for AOL, dismissed concerns over the security of its Internet service, which has 27 million users.

"We track these issues, and we've not seen any significant reports of this Trojan," said Weinstein.

He wasn't willing to explain how the Internet provider tracked virus infection, and said that AOL itself doesn't, and wouldn't, scan its users' email for viruses because it "didn't want to open users' email", a not altogether satisfying explanation.

Weinstein said AOL provides a forum for members to download antivirus software and also took steps to educate its users, for instance by advising them not to open suspicious email attachments.

McAfee is one of the providers of this service and surely it wouldn't issue an alarmist alert in order to draw attention to its software amongst AOL's huge user base? Perish the thought. ®

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Network Associates facts and figures