Microsoft has pulled four of its eight security patches scheduled for tomorrow.

The company has announced that it would no longer be offering three 'important' patches that addressed vulnerabilities in Windows, the Office business software suite and Visual Studio and a fourth one, that also addressed a Windows vulnerability, that the company rated as "critical."

Microsoft said it still planned to release the remaining four patches. Three of them affect Office and one affects Windows; each is rated "critical."

"Critical" is the highest level of urgency on Microsoft's ranking system, indicating that the vulnerabilties could be exploited to run malicious software on a PC with no action on the part of the victim.

Asked for an explanation of the sudden change, a company spokesman only said, "There are many factors that impact the release of a security update, and every vulnerability presents its own unique challenges."

Original reporting by IDG news service