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US software giant Microsoft rushed out a fix for a security flaw in its Internet Explorer Web browser after attackers had begun exploiting the vulnerability to take control of computers, an Associated Press report said.

According to the report, the Redmond-based software maker said it was putting out the fix ahead of the next scheduled security fix release date on October 10 because of the severity of the problem.

The flaw carried Microsoft's highest "critical" rating, the report said.

The vulnerability in Microsoft's browser was particularly worrisome to security experts because computer users could come under attack just by visiting a Web site that had been manipulated to take advantage of the flaw, the report said.

That, in turn, would give an attacker complete control of a user's computer, including access to emails, personal information and other data.

Johannes Ullrich, CTO with the security research organization SANS Institute, said it appeared that a couple of thousand Web sites had already been manipulated to launch such attacks. The attack also seemed to be spreading via email, he said.