On May 14, 1988, most computers attached to the Israel University had their hard disks corrupted. It was reported that nearly 115,000 disks were corrupted on that day. Later on, it was found to be a virus that was programmed to change the system areas of all accessible hard disks. This virus was named the Jerusalem Black Hole virus.
In another incident, people purchasing BASIC programs suddenly found that characters on the screen started bouncing up and down. This was attributed to a virus known as the Italian Ping-Pong virus.
These are just two of the numerous news items related to computer viruses, which you have probably read. One of the buzzwords in the field of computers today is virus. A virus is an actively infectious computer program that places copies of itself into other applications and programs. It also infects data files and documents. The reason why a virus attaches itself to an executable program is that, in order to perform its destructive action, it has to get executed. Thus, it remains dormant until you run the application or program to which it is attached. Viruses, which infect document files, load the virus code into the RAM whenever the document is read.
Typically, on running the program to which a virus is attached, the virus infects all portions of memory and then infects other files on your disks (diskettes and hard disks). So the next person using the same diskette on a different computer spreads the virus to the new system.
The reason why viruses cause so much fear is that they destroy valuable data and programs, which could mean that you loose months of work.
When PCs have been connected together to form a network, the damage can be worse. This is because the virus program spreads from one PC to another, thus infecting all the workstations (the computers that form part of the network).