The security patch Microsoft recently released against a flaw in the HTML Help ActiveX part of Windows does not address a newly discovered hole in the system.
Users of Windows XP are vulnerable, even if they are using fully patched versions of Service Pack 1. Windows 2000 running a fully patched Service Pack 4 are also at risk from the vulnerability which could allow a hacker to place malicious code, including spyware, on a system.
The new flaw was discovered by GeCAD NET, a Romanian security company whose anti-virus software business was recently bought by Microsoft.
Microsoft has admitted that there is a new flaw, although it did not say when it will bring out a patch for the new threat.
GeCAD NET said users who had already downloaded the patch against the original threat on the two affected systems were now open to attacks. Users of Windows XP Service Pack 2 do not appear to be affected, said GeCAD NET.