If you receive an Instant Message containing the following link, do not click it.
It does not link to a video file. If you click it, you will download an exe file to your computer, which will send the link to everyone on your buddy list repeatedly.
Edit: There's been an update. There are now several links passing around, but all of them still have the signature "-s" after the link.
If your friend says "-s" after giving you a link, do not click it.