STOPzilla is now part of RealDefense product portfolio. Learn More

How Computer Viruses Work

What Are Computer Viruses?

Computer viruses are malicious programs that hog system resources and execute undesirable functions. There are many types of computer viruses, and they each work differently in the ways they replicate and/or spread. You may find this information helpful for avoiding computer viruses online, or identifying viruses that have infected your system.

Computer Viruses


A virus is a small piece of software that piggybacks on real programs. For example, a virus might attach itself to 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) or wreak havoc on your computer.

Email Virus

Email viruses:

An email virus travels as an attachment to e-mail messages, similar to how the above virus attaches to programs. Email viruses work by automatically mailing themselves to people in the victim's email address book. Some email viruses don't even require a double-click – they launch when you view the infected message in the preview pane of your email software.

Trojan Horse

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 (such as erasing your hard disk). Trojan horses have no way to replicate automatically.

Computer 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.

How Can I Protect Against Computer Viruses?

STOPzilla AntiVirus uses our proprietary AntiVirus Technology to target all types of computer viruses. With one of the most extensive virus and malware databases in the industry, STOPzilla scans deeper and more thoroughly than other security products. It finds and eliminates many threats that other products in the industry fail to detect.