Microsoft will release six groups of security patches next week, including three critical updates for Windows and Excel users.

The critical updates will fix bugs in many different versions of Microsoft's products, including the latest versions of Excel, Windows XP, Vista, and Windows Server 2003, Microsoft said Thursday in a note on its Web site.

Online criminals have used flaws in Excel and other Microsoft Office products in limited attacks over the past year. Typically, the attacker will e-mail the victim a maliciously encoded Office attachment. If the document is opened, the hacker can then gain access to the victim's computer.

Microsoft isn't releasing further details on the flaws it's fixing until Tuesday, but it rates an update critical if it fixes a vulnerability that could be used by a hacker to remotely install unauthorized software on a victim's computer.

Three other less-critical updates are also planned for next week's "Patch Tuesday" security fixes.

They include "important" updates for Microsoft Publisher 2007 and Windows XP Service Pack 2 as well as a fix for Windows Vista.

In descending order of severity, Microsoft rates updates as critical, important, moderate, or low.