Microsoft on Tuesday warned users of its Windows operating system of two "critical" security flaws in its software that could allow attackers to take complete control of a computer.

The world's largest software maker issued patches to fix the problems as part of its monthly security bulletin. The problem mainly affects the Windows operating system.

The warning came after the company last week made a patch available earlier than expected to fix a different critical flaw in the Windows operating system.

Computer security experts and Microsoft urged users to download and install the patch available at www.microsoft.com/security.

Microsoft defines a flaw as "critical" when the vulnerability could allow a damaging Internet worm to replicate without the user doing anything to the machine.