Read more about it (and how to protect your computer) at the about.com site.
Also, please take the following steps immediately to protect your computer until Microsoft figures out how to fix the problem:
- Disable Google Desktop if you have it
- Disable Picasa if you have it
- Disable HTML in your email client
- Do not open email attachments with names ending with .wmf, .jpg, .jpeg, .bmp, .dib, .gif, .emf, .jiff, .jpe, .png, .tif, .tiff and of course, .scr
- Disable images in your browser (for gawd's sake, if not your own, PLEASE shift to Mozilla Firefox IMMEDIATELY) when you visit unknown sites (like, when you do a search)
Better safe than sorry.