Users of the world's most common web browser have been advised to switch to another browser until a serious security flaw has been fixed.
The flaw in Microsoft's Internet Explorer could allow criminals to take control of people's computers and steal their passwords, internet experts say.
Microsoft is investigating the problem and preparing an emergency software patch to resolve it, it says.
Internet Explorer is used by the vast majority of the world's computer users.
"Microsoft is continuing its investigation of public reports of attacks against a new vulnerability in Internet Explorer," said the firm in a security advisory alert about the flaw.
Microsoft says it has detected attacks against version seven of the browser - its most widely used edition.
But the company warned that other versions were also potentially vulnerable.
“That made me feel very special and underlined to me that Ulster is more than a team, it is a community and a rugby family" Rory Best
you wont look back, firefox is faster, awesomely customisable and with addons like noscript you will never pick up malicious code from websites unless you allow it.
only down side is the slower load time than IE but thats because parts of IE loads up in the background when you start windows.
Microsoft plans quick fix for IE
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.
Potential danger
According to Rick Ferguson, a senior security adviser at security firm Trend Micro, the flaw has so far been used to steal gaming passwords but more sensitive data could be at risk until the security update is installed.
MICROSOFT SECURITY ADVICE
Change IE security settings to high (Look under Tools/Internet Options)
Switch to a Windows user account with limited rights to change a PC's settings
With IE7 or 8 on Vista turn on Protected Mode
Ensure your PC is updated
Keep anti-virus and anti-spyware software up to date
"It is inevitable that it will be adapted by criminals. It's just a question of modifying the payload the trojan installs," he said.
It is relatively unusual for Microsoft to issue what it calls an "out-of-band" security bulletin and experts are reading the decision to rush out a patch as evidence of the potential danger of the flaw.
Some experts have suggested that users switch browsers until the flaw is fixed.
Firefox, Opera, Chrome and Apple's Safari system are not vulnerable to this current flaw.
But Graham Cluley, senior consultant with security firm Sophos, said no browser is exempt from problems.
"Firefox has issued patches and Apple has too. Whichever browser you are using you have to keep it up to date," he said.
"People have to be prepared and willing to install security updates. That nagging screen asking if you want to update should not be ignored," he said.
“That made me feel very special and underlined to me that Ulster is more than a team, it is a community and a rugby family" Rory Best