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What is a virus?
    Simply put, a virus is a type of software that "infects" a computer. It's typically inserted into a program, and when that program is executed, the virus activates and attaches itself to other programs in your PC. Viruses can be a simple prank--an annoying pop-up message or blue screen, for instance--but too often a virus is a malicious attempt to outright destroy data and programs.

    There are several different types of viruses, but they all have a common thread that you should remember: Viruses aren't actually attached to data; they must be run in some form to infect a PC or its data. For instance, boot viruses are stored on floppies and infect a PC when the floppy is left in the drive during boot. Upon startup, the virus launches and then spreads to other floppies and wipes out data. Macro viruses are hidden within documents or data, and unleashed when the macro is run. Viruses also commonly come in the form of Web downloads and e-mail attachments, embedded in EXE, VBScript or database files.

    But no matter what form it's disguised in, the virus must be triggered in order to run. So if you receive an e-mail attachment with a virus, for instance, as long as you don't open (run) the message, you should be safe. Delete the message immediately if you suspect a virus.

    Viruses can infect and destroy immediately, or launch on a specified date. They can affect single desktops, or spread to entire networks, servers and Web sites. While many viruses are simply pranks or annoyances, others are more complex and their effects can be devastating. Viruses can obliterate data, corrupt programs so that they no longer run, stall servers with e-mail bombs, and--in the case of the "I Love You" worm virus--replace files, steal passwords and infect address books as it propagates itself.

What are the different kinds of viruses?

This is a list of some of the more popular versions of computer viruses:

Boot Sector Computer Viruses
The boot sector viruses was a whole lot more popular in the eighties. This was when computer technology actually hit the mainstream. Quite like the name, boot sector viruses infect the boot sectors of a computer. These boot sectors are usually located in the bootable disk or in particular location in your computer hard drive. A number of these boot sector viruses in the past include names such as Disk Killer and others like Michelangelo. The damage caused by boot sector viruses can be devastating, varying from individual file loss to entire directories .

Companion Viruses
These sorts of viruses usually affect your computer by infecting your computers operating system. They work by creating a dangerous program that looks like the other valid files that are on your computer. These programs accompany other files that exist on your computer, so you may end up executing a virus instead of the program that you really wanted to run. These types of viruses can wait in memory for a program to run and can easily replicate.

Email Viruses
These sorts of viruses use e-mail in order to transmit viruses from one computer to the other. Someone may send you an e-mail that has an attachment that has a virus in it. When you open the attachment your computer gets infected. Some of them actually copy themselves to all the e-mail addresses in your address book and the virus gets to spread as quickly as it can. Avoid opening e-mails from anyone that you don't know. Some e-mail programs actually now come with the capability to scan through attachments with antivirus programs. They can easily identify any virus programs before you would even spot them.

Macro Viruses
Macro viruses are small programs which can infect files created with certain applications, including word processing and spreadsheet office suites. These little programs can take advantage of the program's built in macro programming tools to perform maliciously.

Polymorphic Viruses
Polymorphic viruses actually will hide themselves each time they infect a system, making it nearly impossible to be detected by anti-virus string or signature searches. Because these types of viruses encrypt or encode themselves differently every time, they are more difficult to detect and are able to easily replicate large numbers of new instances of themselves. Basically it adapts, changes its own code, and replicates all on its own.

Trojan horse viruses
Trojan horse viruses are actually malware, they are usually thought of as viruses because of the amount of damage that they can do to your computer. These viruses are actually quite tricky; they appear as something as innocuous as a screensaver or game. When you install the program you end up with a virus on your system. The virus may then leave a backdoor for hackers to enter into your computer. When these hackers enter they can then proceed to steal personal information such bank account and credit card information, and even passwords. This is one of the more common viruses seen today.

Worm Viruses
Worm Viruses have the ability to easily and quickly duplicate themselves, occupying tremendous amounts of computer resources while it wreaks havoc on your computer and network.

If you want to protect yourself from computer viruses such as the types listed above. It is absolutely essential that you obtain the best protection software available. We recommend using Sophos Virus scan. It's important to make sure your anti-virus software is as up to date as possible, as new infections are discovered each day. You may also want to invest in a firewall that helps prevent other people accessing your computer. Once a computer is infected with a virus, it is unsafe to keep using this system; it can damage files and send to your contacts through email. You should also make regular backups of your data and keep this unconnected to your system, to restore your files if necessary.