There's a new zero-day attack in progress against Yahoo Messenger users. The instant messaging solicitation invites users to open their Webcam. However, the code used in this China-based exploit causes a heap overflow to be triggered when the target accepts a Webcam invitation. That means a remote attacker could execute malicious code on a compromised machine.
The McAfee security blog recommends the following: do not accept Webcam invites from untrusted sources until a patch is released, and block outgoing traffic on TCP port 5100 on your firewall until a patch is released.
Yahoo has been informed and says it is working on a patch.