As part of its monthly patching cycle, Microsoft plans to release on Tuesday one security bulletin for the Windows operating system.

The security bulletin is deemed "critical," Microsoft's highest risk rating, the company said in a notice posted on its Web site on Thursday. Last month's "Patch Tuesday" included nine bulletins covering 14 Windows flaws. Some of the patches have caused trouble for users since their Oct. 11 release.

Microsoft rates as critical any security threat that could allow a malicious Internet worm to spread without any action required on the part of the user.

Microsoft's notice did not specify which component of Windows is being repaired in Tuesday's bulletin or how many flaws the update will deal with. Security researchers have several unpatched flaws outstanding with Microsoft. For example, eEye Digital Security lists eight vulnerabilities on its Web site for which it considers fixes overdue.

In addition to the Windows security fixes, Microsoft also plans to issue at least two updates that it deems high priority, but that are not security-related, the company said.

Furthermore, as it does every month, a new version of the Windows Malicious Software Removal Tool will be released. The tool detects and removes malicious code placed on computers.

Microsoft gave no further information on Tuesday's bulletins, other than stating that the Windows update will require restarting the computer.

The Redmond, Wash., software giant provides information in advance of its monthly patch release day, which is every second Tuesday of the month, so people can prepare to install the patches.

Microsoft said it will host a Webcast about the new fixes on Wednesday at 11 a.m. PDT.