Microsoft has released a dozen patches covering 19 newly discovered security flaws, the bulk of which are rated as 'critical', for its operating systems and applications.

The most serious flaw is in patch MS05-011, which covers server message blocks, found in Windows 2000 and above.

The flaw could allow a worm like Sasser to cripple IT systems as it allows hackers to take full control without the need for a user to take any action.

"An attacker who successfully exploited this vulnerability could take complete control of an affected system," Microsoft confirmed today.

"An attacker could then install programs, view, change, or delete data, or create new accounts with full user rights. We recommend that customers apply the update immediately."

Of the other patches most are for versions of operating systems going back to Windows 98, with additional application patches for Office, SharePoint Services, Windows Media Player, MSN Messenger and Internet Explorer.

In a worrying sign for Microsoft's security plans, six of the patches deal with code that was updated in Windows Service Pack 2.

The pack, 80 per cent of which was security oriented, was intended to make both Microsoft's XP operating system and Internet Explorer more robust and secure.

Microsoft's Windows Security Updates Summary for February 2005 and the relevant patches can be found here.