Microsoft has given advanced notification of four security patches in this month's Patch Tuesday on 13 May.

The update will include fixes for vulnerabilities in Microsoft Office, Windows and OneCare.

Three of the vulnerabilities have been rated 'critical', Microsoft's highest security level. A fourth was rated 'moderate'.

Two of the critical flaws lie in Microsoft Office. Versions affected include Office XP, 2000, 2003 and 2007. The 2004 and 2008 versions of Office for the Mac will receive patches for critical flaws.

The third critical fix will be applied to a flaw in Windows 2000, XP and Server 2003. Barring a last-minute addition, Vista and Server 2008 will not be affected by the update.

The lone 'moderate' fix will apply to security products Windows Live Onecare, Windows Defender, Microsoft Antigen, Forefront Security and Standalone System Sweeper.