Microsoft is currently dealing with an exploit (KB2847140) for a 0-day vulnerability in Internet Explorer (IE). Machines attacked by this exploit will yield full control to the attacker and allow him to install more advanced malware such as the well known RAT Poison Ivy. The exploit was first discovered last Wednesday on a website of the Department of Labor specialized in nuclear technology. It has since spread to other websites and is now also available in Metasploit. The exploit works only against IE version 8 (IE8), which limits the exposure to about 42% of all systems, according to last count from our BrowserCheck service.
IE8 is the latest version available on Windows XP, and was also the original version installed on Windows 7. This explains the rather high numbers that we are seeing for this older browser. Windows 7 users have access to IE9, which is not affected by this attack and has a much better security architecture. Upgrading to IE9 is a straightforward way to defend against the attack.