What exactly is a computer virus?

Answer

Dear Tibo

Actually, a computer virus is a “normal” program and can therefore not really destroy your computer, at least if you mean the fixed parts of your computer, such as the processor, the hard disk, the memory, …

What a virus can do, and what it likes to do, is waste so much time doing pointless things that make your computer run very slow, or destroy all your computer’s files, or clutter your hard drive; or cause a lot of internet traffic. After all, those are things that a “normal” program does: when Word’s spell checker works, other things happen slower; Word also changes files on your computer (namely the texts you work with) and Word also puts “junk” on your hard drive (especially some temporary files).

But of course, a virus is primarily a “naughty” program, and it does nonsensical or naughty things that stop your other programs from working properly. Moreover, the virus writer mainly wants his program to end up on as many computers as possible. Therefore, a virus will start to replicate itself. It does that by joining the other programs on your computer. For example, a virus can modify the file of your Word, Firefox or any other program so that the virus runs first and then the “real” program. In this way, as a user, you do not immediately notice that the virus is running, but it does happen.

Moreover, a good virus ensures that it does not immediately destroy all programs on the computer: if it did, it cannot spread properly.

Viewed in that way, such a program is similar to a biological virus that attacks humans, for example. Such a virus also ensures that it can spread as well as possible from person to person, but at the same time ensures that people do not die immediately. Because a dead person can’t spread viruses very well, while a walking person can.

In summary, a virus is an “ordinary” program that modifies files in order to spread itself as much as possible.

If you want to know more about this, you can google “Fred Cohen” and his 1984 paper “A Computer Virus”.
Or you can read my piece of course in the attachment. This is not a difficult course at all, very readable and you should not be afraid 😉

Kind regards