Computer crime has been a growth industry during the last thirty years. Much of the best known instances seem not to be financially motivated but that is not to say that they are not financially damaging to the victims. In addition, those into crime for financial gain are beginning to realise that computers provide a wealth of opportunity. Fighting Computer Crime includes numerous examples of existing crime as well as speculating on what may happen over the next few years. Clearly it cannot go into details of defence mechanisms but it can and does cover areas of danger and simple steps to protect yourself.
Intrusion detection is concerned with network security.
The police regularly encourage you to consider the security of your house. We all know a range of simple steps to take in that area, and I think most understand that the primary objective is to make it more attractive for criminals to go elsewhere. Banks can afford vaults with feet of reinforced concrete, steel doors inches thick, governments can afford even more but householders can usually only afford to deter. The same spectrum applies to networks. You will not stop every hacker from reaching into your network so you need other lines of defence.