Using leak tests to evaluate firewalls

A well-designed firewall should not allow any leaks. It should be able to detect all attempted inbound and outbound network activity. This is why two criteria are used when analyzing the quality of protection provided by a firewall: the quality of inbound protection, i.e. protection against penetration from outside the network and the quality of outbound protection, i.e. protection against data leaks sent from the computer.

Read the article HERE.