Computer (1) is an intrusive (2) that infects computer (3) by inserting (4) of itself in those files. The copies are usually executed when the file is loaded into (5) , allowing them to (6) still other files, and so on. Viruses often have damaging side effect s sometimes intentional, sometimes not -- such as destroying a computer's hard (7) or taking up (8) space that could otherwise be used by program . A virus is a program, made by either a (9) or not. It is not so easy to make one, but many people know how to do it, for example, you may know that you have to know some exact computer (10) to make a computer virus .