Firefox is a very popular browser with Linux users, and it even comes installed by default on many Linux distros. Therefore, the scale of the following problem is potentially quite large; a new vulnerability with Firefox that might allow hackers to seize control of Unix or Linux machines running vulnerable versions of the browser has been discovered. The problem has been confirmed on version 1.0.6 of Firefox on Fedora Core 4 and Red Hat Enterprise Linux 4, and could lead to a means for hackers to execute arbitrary shell commands. To do this, an attacker would have to trick users into following a malicious link in an external application that uses Firefox as the default browser. There is no evidence that the security bug is being actively exploited at present, but the worry is there none the less.