There's what's known as a 0-day Windows exploit (exploit discovered before a patch is ready) in the wild. Some websites are already exploiting it, and it's only a matter of time before it becomes an exploit used in email (whether as spam or as the product of an installed virus) and files.

This is a hack of the Windows MetaFile format - Thus all Windows machines are vulnerable, and this is a cross-browser suseptibity.

Snippet from the page: "Note that this WILL temporarily disable the "Thumbnail" view in Windows Explorer and Window's Image and FAX viewer. This is by design, since these viewers are no longer safe to use until a non-vulnerable file has been produced by Microsoft and installed."

For details, go here. This page also includes details on how to disable the vulnerable component.

It is recommended that you reboot after disabling the component to prevent anything already in memory from being affected.