A computer virus is a program which, after being loaded into a computer's memory, copies itself with the purpose of spreading to other computers.
Most people, from the corporate level power programmer down to the computer hobbyist, have had either personal experience with a virus or know someone who has. And the rate of infection is rising monthly. This has caused a wide spread interest in viruses and what can be done to protect the data now entrusted to the computer systems throughout the world.
A virus can gain access to a computer system via any one of four vectors:
1. Disk usage: in this case, infected files contained on a diskette (including, on occasion, diskettes supplied by software manufacturers) are loaded, and used in a previously uninfected system thus allowing the virus to spread.
2. Local Area Network: a LAN allows multiple computers to share the same data, and programs.
However, this data sharing can allow a virus to spread rapidly to computers that have otherwise been protected from external contamination.
3. Telecommunications: also known as a Wide Area Network, this entails the connection of computer systems to each other via modems, and telephone lines. This is the vector most feared by computer users, with infected files being rapidly passed along the emerging information super-highway, then downloaded from public services and then used, thus infecting the new system.
4. Spontaneous Generation: this last vector is at the same time the least thought of and the least likely. However, because virus programs tend to be small, the possibility exists that the code necessary for a self-replicating program could be randomly generated and executed in the normal operation of any computer system.
Even disregarding the fourth infection vector, it can be seen that the only way to completely protect...