It exploits a Windows MetaFile weakness that was fixed months ago, but if you ran IE and didn't install the fix, your computer got served with adware!
WHEEE!
http://blog.washingtonpost.com/securityfix/2006/07/myspace_ad_served_adware_to_mo.html
WHEEE!
http://blog.washingtonpost.com/securityfix/2006/07/myspace_ad_served_adware_to_mo.html