Microsoft has issued an emergency security patch for its Internet Explorer browser after a flaw that could let hackers access users' computers and steal passwords was discovered.
Software security firm Trend Micro says as many as 10,000 Web sites may have already been infected with malicious software.
When one of these sites is accessed with Internet Explorer, keylogging software is automatically installed on the computer that can record data.
Most of the compromised sites are Chinese, with attackers attempting to steal computer game passwords that can be sold on. However, the flaw opens the possibility of bank passwords, credit card details and other financial information being stolen.
The security patch includes more than 300 updates for more than half-a-dozen versions of IE in around 50 languages.