Microsoft is due to issue a patch to fix a security flaw believed to have affected as many as 10,000 websites.

The emergency patch should be available from 1800 GMT on 17 December, Microsoft has said.

The flaw in Microsoft's Internet Explorer browser could allow criminals to take control of people's computers and steal passwords.

Internet Explorer is used by the vast majority of computer users and the flaw could affect all versions of it.

So far the vulnerability has affected only machines running Internet Explorer 7.