The security flaw affects millions of internet explorer browser users.Microsoft said attackers can exploit the bug to infect the PC of somebody who visits a malicious website and then take control of the victim's computer.
Some security experts said it would be too cumbersome for many PC users to implement the measures suggested by Microsoft. Instead they advised Windows users to temporarily switch from Internet Explorer to rival browsers such as Google Chrome, Mozilla Firefox or Opera.
Symantec and other major anti-virus software makers have already updated their products to protect customers against the newly discovered bug in Internet Explorer.
Internet Explorer was the world's second-most widely used browser last month, with about 33 percent market share, according to StatCounter. It was close behind Chrome, which had 34 percent of the market.