Microsoft has scratched half of the security updates it announced last week, and will now release only four sets of patches Tuesday morning.

On Friday, the developer updated its monthly advance bulletin to say that it would issue just four updates Jan. 9: one for Windows and three for Microsoft Office. Dropped were two security updates for Windows, one that was to affect both Windows and Office, and another that involved both Windows and the Visual Studio 2005 development platform.

At least half of Tuesday's updates will be labeled "critical," Microsoft's highest threat ranking.

"We continue to plan to release the 4 remaining bulletins," said Mike Reavey, operations manager of the Microsoft Security Response Center (MSRC), in a message on the team's blog.

A Microsoft spokesperson would only add that "There are many factors that impact the release of a security update, and every vulnerability presents its own unique challenges," when asked to explain the update changes.

This is the second month in a row that Microsoft has changed its mind about security updates; in December 2006, it added a pair of patches for Windows Media Player at the last minute.

The four remaining security updates will be available for manual download from the Microsoft Web site Tuesday about 10 a.m. PDT. As usual, automatic updates to users' computers will begin shortly after that.