Servers can also be protected with intrusion detection software. Like motion detectors in a building, but much more sophisticated, these software packages running on a server can recognize unauthorized or unusual actions on the computer and sound an alarm as well as putting a stop to the behavior. Intrusion detection software can also correct changes, such as replacing a modified web page with the correct original. A scanner is a less elaborate kind of intrusion detector. Intrusion detectors and scanners may also be used on the inside network itself.
Insiders perpetrate most computer crimes, mandating monitoring of the inside network.
Also, because users of a network can unintentionally introduce insecurities, network intrusion detection devices can be used to keep watch on the security perimeter, making sure it is unchanged, making sure it is intact. Speaking of the network, the information that flows over that network is also vulnerable to attack through snooping or eavesdropping. Again here, to protect the privacy of the data, we employ encryption. On the Internet The final domain of security is the network security perimeter, protecting a private network from outsiders while giving some access to the Internet from the private network. On the scene for two or three years, they are just recently coming into common use.