Some flaws (or rather, some more flaws) in IE have been rated by security experts as "extremely critical". These flaws, of which there are three, concern the way Internet Explorer renders web pages, and were discovered by various US computer security researchers. It is feared that they could be used to break into a computer running IE, using a specially crafted web page.

On 21 December 2004, several months after discovering one of the flaws, an independent US computer security team called GreyHats Security Group published code showing exactly how to use the flaw to hijack a computer.

Microsoft has yet to release a software fix for any of the problems and US computer security firm Secunia raised its threat assessment for all three flaws to the most severe on Friday.