Microsoft plans to deliver a record 14 security updates next week to patch a record-tying 34 vulnerabilities in Windows, Internet Explorer (IE), Office and Silverlight.
But people still running Windows XP Service Pack 2 (SP2) will receive only a few of those fixes.
Eight of the 14 updates were labelled with Microsoft's "critical" label, the highest threat ranking in its four-step scoring system. The remaining six were marked "important," the second-highest rating.
Next week's Patch Tuesday will be a record on several fronts.
The 14 updates are a record, beating the count from both February 2010 and October 2009 by one. The 34 individual patches equals the single-month record, which was first set last October and repeated in June 2010. And the eight critical updates next week will also tie the record set in October 2009.
"This is big, not only because of the numbers, but also because they'll affect everybody," said Wolfgang Kandek, CTO of security risk and compliance provider Qualys.
According to Microsoft's monthly advance notification, the company will deliver 10 updates for Windows, half of them critical, the other five rated important. Two updates will patch one or more critical bugs in IE and Silverlight, while another pair affect Office.
All currently-supported versions of Windows are impacted by multiple updates, Microsoft said, with Windows XP Service Pack 3 (SP3), the oldest edition that receives patches, affected by all five Windows-only critical updates, as well as by the critical IE and Silverlight fixes.
Nor will Windows 7 escape next week: two of the five critical Windows updates apply to the newest operating system, as do the critical IE and Silverlight patches. Windows 7 will receive at least 10 of the 14 planned updates.
The Office updates are aimed at flaws in Word and Excel, and affect all versions of the word processor and spreadsheet with the exception of those in Office 2010. Both updates also apply to the Mac editions of Word and Excel, said Microsoft.
"A large month was expected," said Kandek, "but my main worry now is for Windows XP SP2 users who haven't upgraded."
Last month, Microsoft retired Windows XP SP2 and Windows 2000 from "extended support," which means security patches will no longer to crafted or supplied for those operating systems.