Microsoft on Monday unexpectedly added two more critical security updates to the list it will deliver tomorrow, including one for all versions of its Internet Explorer (IE) and another that will affect the soon-to-be-retired Windows XP.

"These updates have completed testing and will be included in tomorrow's release," said Dustin Childs, a spokesman for Microsoft's Trustworthy Computing group, in a short addendum to a blog originally published last Thursday.

Then, Microsoft said it would have just five security updates, two critical, that would quash vulnerabilities in Windows and the company's Exchange-based Forefront Protection 2010 security software.

The last-minute addition of two more critical updates, which brought the total to seven, four of them with Microsoft's highest-level threat rating, was unusual, said Andrew Storms, director of DevOps at San Francisco-based CloudPassage. But he took Childs at the latter's word about why the new ones squeezed onto the slate.

"They were probably busy testing the new updates, but hadn't confirmed they were good until this morning," said Storms in an interview conducted using instant messaging.