Firefox has been compromised. Internet users looking for a US Green Card are at risk of being conned by a fake advertisement that will install an adware-laden version of Firefox. Regardless of what version of Firefox the user is using, they will be greeted with a warning that their browser is out of date and encouraged to download and install a new version of Firefox.

"The browser build appears to be genuine, however it has been compromised with a multitude of add-ons, adware, toolbars and other malicious and irritating accompaniments that will find their way onto the user’s PC as part of the install," Christopher Boyd, a senior threat researcher at ThreatTrack Security, explains.

Digital crap pushed through the scam includes Delta Toolbar, Webcake, Optimizer Pro, QuickShare and an ad for “unlimited cloud storage”, according to a write-up of the scam featuring numerous screenshots on ThreatTrack's website. This crap-ware will have the effect of slowing down your system and littering the desktop.

"If you attempt to install while offline, it won’t work as the install needs to download various components. However, should the install break it will abort but send you to a webpage promoting other offers and installs instead," Boyd explains.

The malicious installer downgrades a user's Firefox browser to version 13 as well installing several PUAs (Potentially Unwanted Applications, otherwise known as crapware). The current version of Firefox is version 23.