What Is The Difference Between A Worm, A Trojan & A Virus

There are a lot of heavily technical terms that get used around computer security. Many of them can be a bit hard to explain in a simple manner, so they often get used incorrectly. One of the most frequently (and painfully) misused groups is the terms that differentiate malware from other types of vulnerabilities and threats. I thought I'd clear up the confusion by explaining what malware, trojans, viruses, and worms are and how they're different from one another.

Here’s the basic definition for all the terms we’ll discuss here:

1. Malware:

This is a big catchall phrase that covers all sorts of software with nasty intent. Not buggy software, not programs you don’t like, but software which is specifically written with the intent to harm.

2. Virus: 

This is a specific type of malware that spreads itself once it’s initially run. It's different from other types of malware because it can either be like a parasite that attaches to good files on your machine, or it can be self-contained and search out other machines to infect.

3. Worm: 

Think of inchworms rather than tapeworms. These are not parasitic worms, but the kind that move around on their own. In the malware sense, they're viruses that are self-contained (they don’t attach themselves like a parasite) and go around searching out other machines to infect.

4. Trojan: 

Do you remember that story you had to read in high school about the big wooden horse that turned out to be full of guys with spears? This is the computer equivalent. You run a file that is supposed to be something fun or important, but it turns out that it’s neither fun nor important, and it’s now doing nasty things to your machine.

5. Vulnerability

Funny thing about software: it’s written by humans. Humans are fallible and sometimes forget to cross t's and dot i's. Sometimes those mistakes create strange behavior in programs. And sometimes that strange behavior can be used to create a hole that malware or hackers could use to get into your machine more easily. That hole is otherwise known as a vulnerability.

6. Exploit

The strange behavior that can be used to create a hole for hackers or malware to get through generally requires someone to use a particular sequence of actions or text to cause the right (or is that wrong?) conditions. To be usable by malware (or on a larger scale by hackers), it needs to be put into code form, which is also called exploit code.