Security researchers have identified an unpatched vulnerability in Windows. The flaw - which affects all supported versions of Windows bar Windows 2003 - resides in a security bug in Microsoft XML Core Services, specifically an unspecified security bug in the XMLHTTP 4.0 ActiveX Control.

The flaw creates a means for hackers to inject malware onto the PCs of surfers running IE who visit a website hosting malicious code that attempts to harness the security bug. Security notification firm Secunia says that the vulnerability is being actively exploited by hackers.