To reduce the risk, limit connections to the outside world. With call-back modems, users must dial into the system, verify their identity, then the modem calls the user back at a predetermined telephone number to establish the connection. Encryption scrambles data into an unreadable format so even if the packets are intercepted, the message remains nonsensical. Upon receipt of the message, only the people who know the private code, or key, can unscramble the data. Virus-detection software will identify many viruses and disable them if possible.
Biometric devices are a rather drastic security measure.
Biometric devices use a person's physical characteristics to verify an identity. The verifying physical characteristic varies. Some use fingerprints, others use voice recognition, others scan a person's retina. Biometric devices are quite costly and are for highly secure environments. A common tool like a protocol analyzer can be hooked up to the network and the intruder can watch all data, including passwords, pass by.