There is a new version of messenger out--this may/may not be related-- but it is due to a
security issue using webcams
You should get the new version to be safe
From Randy F Smith's Ultimate Windows Security
The only patch I'm really concerned about is the one for back level versions of Windows Messenger and MSN Messenger. If your users don't have the very latest version installed you are vulnerable to a remote, arbitrary code hack where in the bad guy takes over your user's computer by initiated a web cam or video conversation. So tell you users not to accept such invitations and to allow the upgrade that Windows proposes the next time they logon to Messenger.