Computer viruses are small programs that hide inside of your computer and then replicate themselves in some fashion in order to spread to other computers. With the internet connecting so many computers to one another, and our propensity to share many of our files with other people, we unknowingly transmit to other computers viruses that have infected our own files. Depending on the design of the virus, once it reaches a computer, it can do almost anything from deleting and corrupting your files, to disabling your computers security measures to make it more vulnerable to a hacker.

Types of Viruses

Computer Viruses can be divided into many different categories; Here are the most common, as well as a brief explanation of each one.

Resident Viruses

This is a type of virus that hides in your computer's RAM memory, controlling and intercepting operations carried out by the system, these are often used to capture passwords and credit card numbers and can corrupt files and programs.

Direct Action Viruses

The main objective of these viruses is to replicate themselves and take a particular action when they are run. When a pre-defined condition is met, the virus will spring into action and replicate itself. These viruses normally attach themselves to other files on your computer, so when the file is run - the virus is activated. Files infected with this type of virus can usually be fixed using anti-virus software.

Overwrite Viruses

When this type of virus infects a file, it deletes all of the information contained within that file and then copies itself into it. In other words, these will gut your files and then wear their clothes. Files infected with this type of virus become useless and can't be recovered without restoring a previous backup.

Boot Viruses

This type of virus infects the boot sector of your disk drives. The boot sector is a part of the disk that stores basic system information and is used to start your computer. These viruses are then loaded on boot-up. Please note that this kind of virus does not affect files. The best way to avoid boot viruses is to write-protect your floppy disks and never start your computer with an unknown floppy disk in the drive. Most antivirus programs can detect and remove these.

Macro Viruses

Certain programs like Microsoft Word, Excel, Access, and Powerpoint have the ability to use small 'helper' programs to extend their functionality and automate repetitive tasks. These 'helper' programs are known as macros and scripts and are stored in the document files instead of the main program. A macro virus is simply a virus that hides out in these files and waits for you to open them with their respective programs - which then run the virus.

File Infectors

This type of virus infects programs and/or executable files. Each time one of these programs runs, the virus is activated; the majority of existing viruses belong to this category, and are classified depending on the actions that they carry out. Think of these viruses as stowaways on your computer's files.

Choosing an Antivirus Software

Antivirus software is one of the most important things you should have on your system. Many PC's come with this software pre-installed, but you should still take a few moments to familiarize yourself with it. There are many available antivirus programs currently on the market. Here, I've compiled some of the best retail and free antivirus solutions for you.

McAfee Antivirus (Retail) - McAfee provides a great antivirus solution. This US based company is maybe the oldest antivirus development company in the world, and in this area experience is king, especially when you're dealing with high-tech menaces.

Norton Antivirus (Retail) - Norton Antivirus, commonly known as Symantec Antivirus, is one of the best antivirus solutions available, even though it's also one of the "heaviest", meaning your system may run slower after installing it, specially if you haven't upgraded lately.

Avast Antivirus (Free!) - Avast Antivirus is a lightweight and free (for home use) solution. They are a newer company but have gained much ground because their software is free and easy to use.

AVG (Free!) - Much like Avast, AVG is a light, easy to manage antivirus package, automatically updated, and provides maybe the best shield protection you may need, without even noticing its presence. What to Do if You Think You Have a Virus

If your computer is running unusually slow, complaining with lots of errors, random reboots, blue error screens, or tons of pop-up windows - chances are good that you have picked up some spyware or a virus.

In this case it's better to stop and think before acting.

What should you do?

1. Stop all your work, close all your files and opened windows.

2. Run your antivirus software to make sure it is operable; do this even before updating it with the latest virus definitions.

3. Update your antivirus with the newest virus definitions and run it again.

4. If your system is still complaining, check it for spyware.

Don't, in any case, start deleting files and programs as you're likely to cause even more harm. This is a good time to backup all your data if you don't have any backups already. Even if you back up data infected with a virus, there is a good chance that it can be recovered and this will spare you from loosing important files if your first effort to identify and remove the virus fails.

What if a Virus Doesn't Let You Access Your Antivirus Software?

If you're getting an error when you try to open you antivirus software, it is very likely the result of a virus on your machine. There are 3 ways to deal with this.

1. Use a rescue disk. Most antivirus programs will ask you to create a 'rescue disk' during their installation, if you did this and know where you put the disk, put it into your PC and reboot. These rescue disks load the antivirus software before any other programs (including windows). If they can load before the virus, then they can find and neutralize it.

2. Use online antivirus software. Many antivirus companies provide free online tools that you can run from their web site's in these emergency situations; Here are just a few: * Avast Virus Cleaner * Kaspersky online virus scanner * Trend Housecall * Panda Activescan

3. Carefully remove your disk drives and install them on another PC, or access them through a network, then use another system to scan the drives.

When to get professional help

If you've been through all of this and your PC is still sinking like the titanic, then it's time to call in reinforcements. Don't have a friend or family member who's a computer whiz? That's ok, because there are plenty of companies which are more than happy to take your PC and clean it up for you, check in your local phone book under "Computers; Repair and Service".

When pricing these services, approach them the same way you approach finding a garage you take your car to - get hourly rates and find a place that will take a look at your PC and give you a free estimate.