Microsoft on Tuesday warned users of its Windows operating system of a "critical" security flaw in its software that could allow attackers to take complete control of a computer. The software maker issued a patch to fix the problem as part of its monthly security bulletin. The problem mainly affects the Windows operating system and Microsoft's Internet Explorer Web browser.

Microsoft's cumulative security upgrade described in bulletin MS05-054 details patches for four vulnerabilities in Internet Explorer and replaces an earlier cumulative update issued by the company in October.

Microsoft said the vulnerability exists in its Internet Explorer Web browser, which an attacker could exploit to take over a PC by running software code after luring users to malicious Web pages.