Firewalls have changed a great deal over the past 20 years. Originally, firewalls were just a simple set of rules to do packet filtering. Though they were not designed to deal with many of the problems that came later, firewalls are still a useful and necessary tool in the security arsenal. Soon administrators needed to identify attacks on the network, stop viruses, stop spam, and block certain types of web traffic. They needed to stop certain applications or monitor and record network activity. Firewalls evolved to meet these needs by adding related network security technologies and content inspection.