From time to time, we pass on warnings about computer virii and worms and security issues and the like. If you haven't heard about this one, you'd better pay attention: it's quite serious and could affect anyone using any form of Windows.
Mac and Linux users, you are excused and may continue feeling superior! You're right!
It might be a good time to stop using Outlook Express and possibly turn off images in your browser controls. And by all means, update your virus software and check in with Microsoft's updates to see when they issue a patch. This one is a very, very big deal, not least of all because you don't have to actually do anything except visit the wrong page, read the wrong e-mail, or view the wrong image.