All the time reports are published about famous and not-so-famous organizations which have had their networks and computers compromized by crackers. These reports are probably only a small percentage of the real problem, since several organizations are reluctant to publish that they have been compromized.
There are several techniques and programs to use to secure your network from exploits from the outside.
Among other it is important to observe the following rules:
This week's security information will especially draw your attention to two excellent papers which describe how crackers work and think. Both papers are focused on UNIX based systems. The general approach however, should be useful whatever systems you use.
Per Olav Førland