Most intrusion-detection products are designed to guard against incoming intrusions. Mr. Gibson either does not understand the difference, or he chooses to ignore it. If users are randomly installing unknown executables, they have many dangers. An executable could decide to erase the entire hard drive. Or, it could package up sensitive information and make an email message that will be sent out the next time the mail client is used.
Trojans are a form of virus.
Normal personal firewalls do nothing about illegal hacking attempts against legitimate programs. At Nervous or higher, the inbound connection to SubSeven v2.2 will not be allowed by BlackICE Defender. SubSeven 2.2 has been very unstable. Our development team is currently working on a patch to BlackICE Defender to better detect SubSeven 2.2. The current version of BlackICE can, in fact, detect SubSeven 2.2, but only under certain conditions.