The director of the FBI's stance is that the Internet was not intended to go unpoliced and that the police need to protect people's privacy and public-safety rights there. Encryption's draw back is that it does not protect the entire system, an attack designed to cripple the whole system, such as a virus, is unaffected by encryption. Others promote the use of firewalls to screen all communications to a system, including e-mail messages, which may carry logic bombs. Firewall is a relatively generic term for methods of filtering access to a network. They may come in the form of a computer, router other communications device or in the form of a network configuration.
Firewalls serve to define the services and access that are permitted to each user.
Another method is to prohibit Telnet access into the system. Change the network configuration when defects become know. Check with venders for upgrades and patches. Audit systems and check logs to help in detecting and tracing an intruder. If you are ever unsure about the safety of a site, or receive suspicious email from an unkown address, don't access it.