In late October, Microsoft announced a critical issue that required an immediate update. Click here for more info.
On Wednesday, Microsoft announced a another vulnerability that allows a malicious user to remotely control your PC without your knowledge, however this time it affects Internet Explorer.
If you haven't already, install the update ASAP on all PCs and servers.
The update may be downloaded from Windows/Microsoft Update or from here: http://www.microsoft.com/technet/security/bulletin/MS08-078.mspx