What is a computer virus?
There are many types of malicious programs such as worms, Trojans, key loggers, and so on. BUT there is only one type of behaviour that defines a computer virus! This is a common misunderstanding in that most people call all these other types of malicious programs “Viruses”.
A computer virus is a program that attaches itself to other executable files such as .exe, .cmd, .com, and so on. It does not destroy the executable file but instead attaches itself to the executable file and possibly all currently loaded executable files in the computers RAM. When that executable file is run the virus is also loaded as well as the intended program which is why you more often than not never even no you have a computer virus running on your computer. The virus must find host executable files to attach itself too since it will not be able to survive as an executable file by itself. This behaviour mimics the behaviour of a biological real life virus and so this is why the name came about “Computer Virus”.
Cleaning infected files?
After the virus has attached itself to the executable file that file is classed as being “infected”. Files that are infected can normally be “cleaned” by a virus scanner because the virus attaches itself to the executable file and so not destroying the executable file. The virus code that has been attached to the file can simply be removed from the infected executable file.
When is cleaning an infected file acceptable?
If the virus is not running on the computer and you have detected an infected file that someone may have sent you you can simply clean the file and then run it and you will be ok. If however you are infected by the virus which is running on your computer you will need a virus scanner to remove it else all executables regardless of how many times you clean them will simply be infected or get re-infected!
What stops a virus re-infecting the same file?
When a virus infects a file it leaves a chunk of code or “signature” in that file which tells the virus that it has already infected that file. Virus scanners have a collection of signatures which are updated weekly which help the scanner to detect a virus inside a file.
What are the effects of a computer virus?
They can be just about anything from destroying a computer to fixing a computer (although they very rarely fix computers). You get some viruses that just fill up your hard drive with rubbish, others that eat up loads of RAM and crash you computer, others that prevent specific applications running, and so on. It is often these effects that reveal a virus may be running on a computer when the computer starts showing strange signs of “illness”.
Why do people create viruses?
Programmers create viruses for many reasons such as; they want the challenge of creating one, boredom and cant think of what else to make, they want revenge on someone and any other reason you can think off!
What virus scanners are available?
There are loads of virus scanners both free and commercial. The best one I have found at the moment is Avast. It is free for personal use and includes many features that paid antivirus scanners provide. There are also online virus scanners that will scan a single file or your whole system all from your web browser. House call is an example of an online virus scanner.
Why keep your virus scanner up to date?
Remember I mentioned virus signatures earlier on? When your scanner says it has just done something like updated its virus definitions database. Then that is what they are referring to. Your virus scanner needs to know what strings of code (virus signatures) to look out for and raise hell over (for the virus) when it finds a signature it recognizes as a virus!
