The company will also release an updated version of its malicious-code-removal tool on Tuesday as part of its monthly security updates.

Johannes Ullrich, chief technology officer at the SANS Internet Storm Center (ISC) in Bethesda, Md., said his company has tested the patches and they appear to be working fine.

'It's really good of Microsoft to have released the patches so quickly,' said Ullrich, whose organization had been recommending that companies download a third-party patch released by a Belgian security expert instead of waiting for Microsoft's scheduled Jan. 10 update.

'So far as we can tell, the [third-party] patch does not interfere with Microsoft's patch,' Ullrich said. But it is better for those who have installed the unofficial patch to uninstall it after they have implemented the Microsoft patch, he said.

'It can only hurt at that point' to have both patches, Ullrich said, adding that SANS's ISC has posted details on its Web site telling users who may have installed any of the earlier patches or work-arounds how to update to the official Microsoft release.