As per a Spanish security researcher, an older version of the QuickTime plug-in causes vulnerability, which primarily targets IE users. [Link].
The attack code that was written by him works with IE on a machine running Windows XP, Vista or Windows 7 that has QuickTime 7.x or the older QuickTime 6.x installed.
Apple is working on releasing a patch for the same. However, IETips.net recommends its users to either uninstalling or disabling the QuickTime plug-in.
However, Symantec recommended that users set the killbit for the QuickTime ActiveX control or rename the plug-in. Instructions can be found on the below Microsoft’s support site:
http://support.microsoft.com/kb/240797