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. Data encryption is the answer. With encryption, data is scrambled before transmission, making it unreadable as it passes over the wire, even if it is intercepted. To scramble or encrypt this data, its bits must be transformed according to an algorithm. The data is transmitted, and at the receiving end, a system of keys is used to decode the bits into intelligible information.