Understanding the Difference Between a Virus, Worm and Trojan Horse

We have all had a computer shutdown or malfunction at one time or another. The common causes for this to happen could be due to having a “Virus”. Did you know that a virus is commonly blamed for computer damage, but that it could also be either a Worm or a Trojan Horse? Today we are going to cover what each one actually is. If you find your computer is being attacked by one of the below it needs to be handled by a professional like myself and eradicated.


A virus attaches itself to a computer program or file, which enables it to spread from one computer to another leaving a sometimes lethal trail. Depending on the type of virus it is there could be mild to severe effects and can hit anything from programs to files. Most viruses are attached to an executable file. It will exist on your computer but cannot infect your computer unless you run or open the malicious program. A virus also requires some type of manual interaction by the user.


A worm is a sub-class of a virus. Worms also spread from computer to computer, but have the capability to travel without human action. It travels unaided and can take advantage of file or information transport features on your system. Worms can replicate themselves on your system. One of my customers recently had a situation where a worm that was received via an email proceeded to email everyone in her database and did just that on a wide scale from there. Having good protection software on your computer can prevent this from happening.

Trojan Horse

A Trojan Horse will initially appear to be useful software, but will actually do damage once installed or run on your computer.  It enters your system when the user is tricked into opening them because they appear to be receiving legitimate software or files from a legitimate source.  Each Trojan has its own design, some can be bothersome while others are very malicious. If a Trojan makes a home on your computer it could create a backdoor on your computer that gives malicious users access to your system as well.

Keep your computer protected at all times by a viable and well updated virus protection software!

Tim Grier
Computer Magician
CET Computer Magic

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