What is a computer virus?
A computer virus is a program designed to spread itself by first infecting executable files or the system
areas of hard and floppy disks and then making copies of itself. Viruses usually
operate without the knowledge or desire of the computer user.
How computer viruses can spread?
When you execute program code that's infected by a virus, the virus code will also run and try to infect
other programs, either on the same computer or on other computers connected
to it over a network. And the newly infected programs will try to infect yet
When you share a copy of an infected file with other computer users, running
the file may also infect their computers; and files from those computers may
spread the infection to yet more computers.
What viruses can do to your computer?
Viruses are software programs,
and they can do the same things as any other programs running on a computer.
The actual effect of any particular virus depends on how it was programmed by
the person who wrote the virus.
Some viruses are deliberately designed to damage files or otherwise interfere
with your computer's operation, while others don't do anything but try to spread
themselves around. But even the ones that just spread themselves are harmful,
since they damage files and may cause other problems in the process of spreading.