Microsoft will issue 12 security patches on Tuesday, with seven of them deemed "critical".
Four of the seven critical patches affect the Office productivity suite.
Alan Bentley, regional VP of security firm Lumension, said, "After several slow Patch Tuesdays, administrators are faced with the most patches they've seen in a year.
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"Because so many critical patches affect so many applications - including Office, Internet Explorer and the operating systems themselves - these are widespread enough to have a bigger effect than we've seen in a year, and they are going to require the utmost attention and energy."