Over the last day, Firefox users may have seen a Add-on related message telling them Firefox is blocking certain Microsoft Plugins.

DO NOT PANIC... It has been caused because of Microsoft releasing more software with a serious security vulnerability. Microsoft released many new updates on Tuesday, and thanks to Windows Update (if you have ii switched on) you would of been given this dodgy update.

"While the vulnerability is in an IE component, there is an attack vector for Firefox users as well," admitted Microsoft engineers in a post to the company's Security Research & Defense blog on Tuesday. "The reason is that .NET Framework 3.5 SP1 installs a 'Windows Presentation Foundation' plug-in in Firefox."

"This update adds to Firefox one of the most dangerous vulnerabilities present in all versions of Internet Explorer: the ability for Web sites to easily and quietly install software on your PC," said the hints and tips site. "Since this design flaw is one of the reasons [why] you may have originally chosen to abandon IE in favor of a safer browser like Firefox, you may wish to remove this extension with all due haste."

According to Microsoft, the vulnerability is "critical," and also can be exploited against users running any version of IE, including IE8.