The antivirus specialists at McAfee have warned of a Trojan that disguises itself as a Firefox extension. The trojan installs itself as a Firefox extension, presenting itself as a legitimate existing extension called numberedlinks.
It then begins intercepting passwords and credit card numbers entered into the browser, which it then sends to an external server. The most dangerous part of the issue is that it records itself directly into the Firefox configuration data, avoiding the regular installation and confirmation process.
The file attached to the email consists of an executable Windows program, the AXM downloader. Once launched, it fetches the extension from the Internet and records itself directly into the Firefox configuration data, avoiding the regular installation process. Firefox extensions are normally distributed as XPI files, which ask the user for confirmation after forcing a pause of several seconds.
You should be extremely careful when installing unsigned Firefox extensions from unknown sources.
Websites were found to be linking to the FormSpy website hosted at IP address 81.95.xx.xx and installing FormSpy using an old VBS/Psyme exploit targeting Internet Explorer. These websites are believed to have been penetrated and modified by hackers
You can read the McAfee info on Formspy here.
Source: Heise Security