Viruses are something we are facing every day nowadays and computers are very exposed if not properly protected. There are many kinds of viruses: Trojan horses, worms, email viruses etc. We’ll see how they work and what how they can affect our computers.

When you listen to the news, you hear about many different forms of electronic infection. The most common are:

Viruses - a virus is a tiny piece of software that piggybacks on real programs. For example, a virus might attach itself to a program such as a spreadsheet program. Each time the spreadsheet program runs, the virus runs, too, and it has the chance to reproduce (by attaching to other programs).

E-mail viruses - an e-mail virus move around in email messages, and usually replicate itself by automatically mailing itself to dozens of people in the victim's e-mail address book.

Trojan horses - a Trojan horse is simply a computer program. The program claims to do one thing (it may claim to be a game) but instead does damage when you run it (it may erase your hard disk). Trojan horses cannot automatically replicate.

Worms - A worm is a small piece of software that uses computer networks and security holes to replicate itself. A copy of the worm scans the network for another machine that has a specific security hole. It copies itself to the new machine using the security hole, and then starts replicating from there, as well.