A virus is a program a piece of executable code that has the possibly of cloning itself. Computer viruses can spread fast and they are hard to eradicate. They can be attached to any type of file and they are spread as files copied and sent from person to person. They can be contacted from a floppy disk or Cd, they can be launched when opening a program or accessing a file, any file, or they can be brought from the internet by downloading a file or accessing a web page and as attachments to e-mails.

Besides replication, some viruses have something else in common: their infecting routine. The behaviors of viruses vary from showing messages or images to destroying files, formatting the hard disk drive and other severe damage. If the virus does not inflict damage it can still cause problems by taking up space and memory, lowering the performances of the computer.

Nine rules for avoiding viruses would be:
1. Use an anti virus program at all times.
2. Install and keep active a firewall.
3. Make sure your system is up-to-date with all the existent updates.
4. Keep your browsers security settings at maximum.
5. Never click yes when your browser asks you if you want to install or open some content coming from an organization you dont know or dont trust.
6. Install an anti-spy ware program to enlarge the protection.
7. Never install a browser help or search bar accepting the times it comes from a reliable source.
8. Use a different credit card for online shopping.
9. Dont click on email attachments that are executable files even if they look as if sent from known persons.

The antivirus programs have a big role in providing your computers security and protecting it from viruses, worms, Trojan horses and other invaders that can attack a computer. The role of an antivirus program is to detect the presence of viruses in a computer, to disinfect the files or delete the ones that cant be disinfected and prevent the contamination of the computer.

Most of the companies that produce antivirus have online free tools for scanning computers for viruses. If you dont have an antivirus yet and cant decide which one to buy you can enter their online sites and try the services for free, then decide what to use.