The history of computer viruses has begun recently, but it has already become legendary. Almost everyone knows a few fables about these creatures but hardly anyone understands what computer virus is.
Viruses are programs that have been written to make a computer behave in an unexpected and undesired way. Although they are often relatively harmless, they sometimes cause a lot of damage. They are usually designed to remain hidden and dormant until a particular time, or until the user performs a particular action, such as pressing a particular combination of keys. They are able to reproduce themselves, and often attach themselves to other programs. It is common for a user to have a virus program on his disk without being aware of it. Plain text e-mail messages cannot contain a virus, but viruses can be carried in e-mail attachments,
e.g. files attached to e-mail messages. Some viruses are much more common than others and are often unknowingly downloaded from a network system such as the Internet.
If you catch viruses, there are anti-virus programs to hunt down and eradicate the virus. The problem is that around 150 new viruses appear every month and you must constantly update your anti-virus package to deal with these new forms.