Hackers are taking advantage of a new zero-day exploit in Internet Explorer 9 and all previous versions, by hijacking the web browser and executing trojans such as Poison Ivy on victims PCs.
The unpatched bug in IE7 to IE9 can be exploited in Windows XP, Vista and Windows 7. Advise has been given to switch web browsers temporarily to Chrome or Firefox (if you are an IE user), as no official patch has yet been released. An official patch will no doubt be included in the next Microsoft Update bulk of patches, which will be automatically downloaded (assuming you have Windows Updates turned on) Today 18/9/2012.
Microsoft are however saying the problem can be solved beforehand using the EMET – Enhanced Mitigation Experience Toolkit v3.0, which is available by a quick Google search