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A computer virus is a programme, or piece of code, that is written to interfere with, and harm, your machine. A virus can replicate itself, spread to other computers, and attack other programmes on your computer. (By attack, we mean change or delete files.) Computer experts distinguish between a virus, a worm, and a Trojan. Here's the differences:
Virus - Can replicate and spread to other computers. Also attacks other programmes
Worm - A special type of virus that can replicate and spread, but generally doesn't attack other programmes
Trojan - Doesn't replicate, but can spread. Doesn't attack other programmes. Usually just a way of recording and reporting what you do on your PC
Viruses are split into different categories, depending on what they do. Here are a few categories of viruses:
Boot Sector Virus
The Boot Sector of a PC is a part of your computer that gets accessed first when you turn it on. It tells Windows what to do and what to load. It's like a "Things To Do" list. The Boot Sector is also known as the Master Boot Record. A boot sector virus is designed to attack this, causing your PC to refuse to start at all!
File Virus
A file virus, as its name suggests, attacks files on your computer. Also attacks entire programmes, though.
Macro Virus
These types of virus are written specifically to infect Microsoft Office documents (Word, Excel PowerPoint, etc.) A Word document can contain a Macro Virus. You usually need to open a document in an Microsoft Office application before the virus can do any harm.
Multipartite Virus
A multipartite virus is designed to infect both the boot sector and files on your computer
Polymorphic Virus
This type of virus alter their own code when they infect another computer. They do this to try and avoid detection by anti-virus programmes.
How do Viruses get on my computer?
The most common way that a virus gets on your computer is by an email attachment. If you open the attachment, and your anti-virus programme doesn't detect it, then that is enough to infect your computer. Some people go so far as NOT opening attachments at all, but simply deleting the entire message as soon as it comes in. While this approach will greatly reduce your chances of becoming infected, it may offend those relatives of yours who have just sent you the latest pictures of little Johnny!
You can also get viruses by downloading programmes from the internet. That great piece of freeware you spotted from an obscure site may not be so great after all. It could well be infecting your PC as the main programme is installing. And if you or your children download software from peer to peer networks (like Kazaa, Morpheus, Shareaza) then you could be downloading more than you bargained for!
If your PC is running any version of Windows, and it hasn't got all the latest patches and updates, then your computer will be attacked a few minutes after going on the internet! (Non Windows users can go into smug mode!)
Could I be infected by a Virus?
If you are infected by a virus, your computer may exhibit some well-known symptoms. Here's a few signs that you may be infected:
Your computer starts running more slowly than it usually does
Your computer keep crashing
Your computer keep crashing and then restarting
Programmes you normally work with suddenly start behaving oddly
You can't access your disk drives
Other symptoms to look out for are strange error messages, documents not printing correctly, and distorted menus and dialogue boxes. Try not to panic if your computer is exhibiting one or two items on the list.
The first thing to do is to scan your PC with your (up-to-date) anti virus software. If your anti-virus software fails to detect anything, then that doesn't mean you're NOT infected - it may just be poor anti-virus software. And remember, most popular doesn't mean most effective. While Norton and Mcafee are good, extensive tests in respected computer magazine show that they are not the best. Not being the best means that they may fail to detect the virus on your PC! Not only that, Norton and Mcafee are becoming really expensive to maintain!
Free Anti-Virus software
There are some good free anti-virus solutions out there. The most popular is AVG. This has gotten results that are as good as the market leaders. You can check it out here (this page also tells you what you DON'T get with the free edition):
AVG Free Edition
Once installed, AVG will update itself on a regular, daily basis. It will also scan emails for viruses, and alert you if it finds anything. The interface is a bit old-fashioned but, hey, it's free and it does a quite a good job!
Another good solution is AntiVir from Avira. The classic edition is free, as well. Check out their website here:
Avira AntiVir Personal Edition Classic
AntiVir will also protect users of non Microsoft computers (Linux/FreeBSD/Solaris). It is, of course, debatable whether you need anti-virus protection if you don't have a Windows machine!
NOTE: If you're changing AV software, you MUST make sure that the old one has been completely uninstalled first. Norton and Mcafee can be difficult to uninstall, and you should consult their website BEFORE uninstalling - they may even have a special tool to do the job. Some people have said that trying to uninstall Norton or Mcafee was worse than getting a virus. (If you see an ad below for either of these two - it's not because we chose it!)
