Networks are particularly vulnerable as they allow a very rapid spread of viruses to all systems connected to the network. A virus can destroy programs and data by erasing files or adding unwanted code to executable programs. Once a program has been infected it serves as a host and the user serves as a carrier. Many USDA agencies are losing staff time to virus origin research and to isolating and eliminating viruses. In most instances the damage is minimal and easily corrected.
Preventive measures reduce the chances of virus infected software invading our systems.
Malicious programs such as Trojan horses and trap doors were originally written for mainframe computer systems. Larger systems without adequate controls are prime candidates for the introduction of malicious programs. Authorized users making unauthorized use of the system may also introduce malicious software to the system. Sound security procedures will help detect and prevent computer viruses and other malicious programs from entering and spreading damage to networked computer systems or personal computers. The guidelines contained in this appendix are adaptable for any type of computer system.