Microsoft has released five new patches, of which three have been given the company's highest alert rating of 'critical', for its operating systems and applications.

Two of the critical patches are for the Windows operating system.

All versions of Windows are affected by an Internet Explorer bug that can allow malware to run on targeted computers by directing users to a specific web page with the code built in.

The second critical flaw affects Windows 2000 and XP. An unchecked buffer in the Workspace section, which allows access to network printers and faxes, can allow hackers to gain administrator privileges on an infected computer.

The third critical flaw, in FrontPage Server Extensions, affects computer running Windows 2000 and above. This fixes a flaw that allows denial of service attacks and buffer overruns in the remote debug functionality of FrontPage Server.

Both Mac and PC versions of Windows are affected by the fourth flaw, rated as important.

The final patch is for users of Excel, Word and Microsoft's Works software. This flaw allows remote code to be run on an infected PC due to problems with the macro handling of the software.

Microsoft moved from a weekly to monthly patching policy eight weeks ago, claiming that the move would make life easier for system administrators to plan patching.

These latest patches were released on 11 November, a public holiday in the US, which meant the US Federal Computer Incident Response Centre had to issue an email warning about them.

Information on all five flaws, and patches to fix them, can be found here.