Frenzied hacker activity around the .ANI vulnerability discovered by Microsoft last week has forced it to issue a patch a week ahead of its traditional Patch Tuesday.

The emergency patch is available today, 3 April, on Microsoft's website.
A stack buffer overflow flaw in Windows' handling of .ANI files allows hackers to inject hostile code into unpatched systems. Internet Explorer can process .ANI files in HTML documents, so Web pages and HTML E-mail messages can also be vectors for the vulnerability.
The Register says hackers were quick to latch on to the potential of the vulnerability creating worms or launching spam campaigns featuring E-mail messages that sought to exploit the security bug.