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Microsoft's MSN Messenger has noted a security vulnerability in earlier versions, including MSN Messenger 6.2, 7.0 and 7.5, and this vulnerability affects Windows Live Messenger 8.0 as well.
The security issue pertained to a remote executionable attack that was being used through accepted webcam or video chat invitations from an attacker. This means that the company has issued a mandatory update for you to upgrade to Messenger 8.1, which is not susceptible to this security vulnerability. Find more details about the malware here. This upgrade has been optional since early on this year, but as the security issue has been made public, the required upgrade has now taken effect.