Microsoft is investigating public reports of a vulnerability in Internet Explorer 6, Internet Explorer 7, and Internet Explorer 8. Internet Explorer 9 and Internet Explorer 10 are not affected by the vulnerability. Microsoft is aware of targeted attacks that attempt to exploit this vulnerability through Internet Explorer 8.
Details of exploit here.
If your Using Windows Vista or Windows 7 then upgrade your browser like you should have done in MARCH of 2011.
If your using Windows XP (REALLY?) then Firefox and/or Chrome FTW.