London, Dec. 16: Users of Internet Explorer, the world’s most popular Web browser, are at risk of having their computers hijacked because of a security flaw.

The flaw allows criminal gangs to take control of people’s computers and steal their personal information when they visit websites that have been corrupted by malicious hackers. It is believed that as many 10,000 sites have been compromised since last week.

Microsoft said that it had detected attacks on machines using Internet Explorer 7, the most widely-used version of the browser, but that other versions are “potentially vulnerable”.

“We are actively investigating the vulnerability that these attacks attempt to exploit,” the firm, which also makes the Windows operating system, said in a security statement. “We will continue to monitor the threat environment and update this advisory if this situation changes.”

By last Saturday about 0.2 per cent of Internet Explorer users had already visited one of the websites designed to exploit the flaw, according a statement on the technology giant’s Malware Protection blog.