This affects all Microsoft servers, such as Microsoft Update and Windows Update, which are user-initiated, and Automatic Updates, which performs the download without user prompting.
"Technical teams are engaged and have been working around the clock to resolve this problem and we anticipate that updates will be made available via the Microsoft Update platform by end of day," Microsoft said in a statement.
"We will post an update when the situation has been resolved and the updates are again available via this distribution channel."
With this security update cycle, Microsoft released 10 security bulletins covering 26 fixes.
It includes four "critical" fixes for Microsoft Office and one "critical" fix for Windows. Critical fixes are considered the most severe and highest risk. Other fixes are rated low to moderate in severity.
Microsoft is once again urging customers to migrate to Windows XP Service Pack 2 with Advanced Security Technologies if they have not done so already. Aside from the new security enhancements in the service pack, Windows XP Service Pack 1 support will end next week.
In addition to the security fixes, Microsoft has updated its Malicious Software Removal Tool to add support for three new nasty bits of malware, Win32/Tibs, Win32/Harnig and Win32/Passalert.