Microsoft has released 13 new security patches on today, including several "critical" updates.

The release, part of Microsoft's regularly scheduled monthly security update, is the company's biggest patch roundup in months. Included are nine Windows updates, with at least one rated "critical". Also in the update bundle is a "moderate-risk" update for Microsoft's SharePoint Services and Office; a .Net framework update rated "important"; a "critical" update affecting Office and Visual Studio; and a "critical" update affecting Windows, Windows Media Player, and MSN Messenger.

Microsoft announced the number of patches in a security bulletin advance-notification message posted to its TechNet website. The company has adopted a schedule of releasing security patches in batches on the second Tuesday of each month.

Microsoft will host a webcast on Wednesday to outline technical details of the updates, followed by a question-and-answer session. This month's webcast has been extended by an hour to allow extra question-and-answer time.