Here's a good article on the different firewall leaktests http://www.pcflank.com/art21.htm
it is a bit dated, but not much has changed since then and most (if not all) of the firewalls will still fail these leaktests even today.
I use System Safety Monitor (a free program) to block applications (such as IE) from accessing the internet without my permission. I believe it would also stop most of these leak tests or a program (i.e. a trojan)designed on them. You can get it here: http://www.snapfiles...stemsafety.html
Also Diamondcs Process Guard (costs $29.95 for a single license) will stop most if not all of these so-called leaktests cold. http://www.diamondcs.com.au
But to be honest their really aren't many, if any, trojans based on the design of these leak tests in the wild today. And your chances are minimal of ever encountering one. Just be careful what you download. Follow the advice given by Cnm. Keep your firewall & anti-virus software up to date. Always pratice safe hex. And you should be ok.
A word of caution:
It is not recommended that you try any of the leaktests (mentioned in the Pcflank article) on your firewall unless you really know what you are doing. Some of them can make changes to your firewall that would compromise your security defenses! And unless you know how to revert those changes it is ill advised to fool around with them. Though a safe leaktest to try is the one at http://www.grc.com/lt/leaktest.htm
called 'leaktest'. All the others should not be used by inexperienced users.
Edited by lonewolf, 06 June 2004 - 05:36 PM.