WHAT IS IT?
There is a new exploit out that uses WMF (windows metafile format) files to infect a computer. All you have to do to get infected is view a webpage that has the image on it, or access an infected image that is on your computer. That means the forums can be a vector for infection too. (In fact, user Blue Reptile has already been permabanned for putting the exploit in his signature.)
WHO IS VULNERABLE?
The exploit affects Firefox, Internet Explorer, and any other browser that displayes or downloads the file into the cache on the local machine. The file could also be a WMF renamed to any other image type, or possible other filetypes. Anything that puts the image exploit onto your computer or opens it up in windows fax viewer or the part of windows that generates thumbnails of WMF files is a vulnerability. This means any vector that puts the image onto your computer (wget, browser, email, IM, etc) can potentially cause the problem.
This affects anyone on Windows (98, 98SE, ME, 2000, XP, 2003). USING FIREFOX DOES NOT ELIMINATE THE RISK as the file is still downloaded to your cache in most cases, but it does reduce your chances somewhat since the image is often not displayed in the browser. But if you then interact with the file in any way (thumbnail it, Google Desktop, hover over with the mouse) that causes it to be handled by the windows subsystem responsible for WMF then you will have problems. Once again, YOU CAN BE CAUGHT BY THIS EXPLOIT EVEN IF THE IMAGE DOES NOT SHOW IN THE BROWSER. If you use Windows, your system is vulnerable.