Yahoo Messenger users beware: Your mother was right when she told you not to chat with strangers. A newly discovered zero-day vulnerability in the widely-used chat program proves this was sound advice.

According to a blog entry by McAfee, company researchers have been able to confirm a report on a Chinese language security forum of a serious vulnerability in the most recent version of the Yahoo chat client. Relying on a heap overflow, it allows bad guys to own a machine simply by getting an unsuspecting Joe to accept a webcam invite.

The vulnerability is reminiscent of nasty bug Yahoo squashed in June that also allowed the remote execution of code on machines using the chat client. That flaw resided in the program's ActiveX control. This flaw is "different," McAfee said, without elaborating.

A Yahoo representative confirmed the vulnerability and said company software developers are scrambling to fix it.

In the meantime, Yahoo Messenger users may want to block outgoing traffic on port 5100. And whatever you do, resist the temptation to accept invitations from people confessing to be lonely, nubile women out for a little webcam fun ®

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