Break-ins and malware are constant threats to computer networks. It's no longer safe to assume that security software will keep all attackers out. An extra layer of defense is necessary, to catch threats that have started to take root and get rid of them as quickly as possible. It isn't unusual for hostile software to sit in a system for months before it's caught. While it's sitting there, it's using up network resources and landing its host on Internet blacklists. Network monitoring can catch abnormal activity and let administrators remove its source.
