# What is the difference between a worm, a trojan and a virus? **URL:** \ **Category:** Factual Questions\ **Created:** [January 31, 2003, 6:08pm UTC](https://boards.straightdope.com/t/what-is-the-difference-between-a-worm-a-trojan-and-a-virus/151910 "2003-01-31T18:08:32Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![Docklands](https://avatars.discourse-cdn.com/v4/letter/d/47e85d/32.png) [@Docklands](https://boards.straightdope.com/u/Docklands)\ **Post date:** [January 31, 2003, 6:08pm UTC](https://boards.straightdope.com/t/what-is-the-difference-between-a-worm-a-trojan-and-a-virus/151910/1 "2003-01-31T18:08:32Z")
Thanks ---
**Author:** ![Urban\_Ranger](https://avatars.discourse-cdn.com/v4/letter/u/e9c0ed/32.png) [@Urban\_Ranger](https://boards.straightdope.com/u/Urban_Ranger)\ **Post date:** [January 31, 2003, 6:10pm UTC](https://boards.straightdope.com/t/what-is-the-difference-between-a-worm-a-trojan-and-a-virus/151910/2 "2003-01-31T18:10:33Z")
A worm is a multicellular organism. A virus isn’t really alive. A trojan is just a wooden horse. 😃 ---
**Author:** ![Bosda\_Di\_Chi\_of\_Tricor](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bosda_di_chi_of_tricor/32/16845_2.png) [@Bosda\_Di\_Chi\_of\_Tricor](https://boards.straightdope.com/u/Bosda_Di_Chi_of_Tricor)\ **Post date:** [January 31, 2003, 6:14pm UTC](https://boards.straightdope.com/t/what-is-the-difference-between-a-worm-a-trojan-and-a-virus/151910/3 "2003-01-31T18:14:09Z")
You wear a Trojan _over_ your worm, to keep from getting a virus. Health 101. Glad we could clear that up. ---
**Author:** ![Ice\_Wolf](https://avatars.discourse-cdn.com/v4/letter/i/dfb087/32.png) [@Ice\_Wolf](https://boards.straightdope.com/u/Ice_Wolf)\ **Post date:** [January 31, 2003, 6:16pm UTC](https://boards.straightdope.com/t/what-is-the-difference-between-a-worm-a-trojan-and-a-virus/151910/4 "2003-01-31T18:16:48Z")
[Definitions.](http://www.geocities.com/TimesSquare/4355/virus-misc/definitions.htm) > [@](#): > > A Trojan horse (a.k.a Trojan) is a program that appears to do something amusing or useful and actually does something else. > \ > A virus is a program that carries out a specific function and infects other programs in the process. > \ > A worm is a virus that does not infect other programs. It still replicates itself to other computers, but will always arrive in the same program. Oh, and **Urban Ranger, Bosda**? 😃 ---
**Author:** ![Docklands](https://avatars.discourse-cdn.com/v4/letter/d/47e85d/32.png) [@Docklands](https://boards.straightdope.com/u/Docklands)\ **Post date:** [January 31, 2003, 6:17pm UTC](https://boards.straightdope.com/t/what-is-the-difference-between-a-worm-a-trojan-and-a-virus/151910/5 "2003-01-31T18:17:43Z")
Comedians. How great! Now I’m going to hug some snakes. That’s right, I’m going to hug and kiss some poisonous snakes. **[sub]Now that’s sarcasm[/sub]** ---
**Author:** ![Ethilrist](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ethilrist/32/4604_2.png) [@Ethilrist](https://boards.straightdope.com/u/Ethilrist)\ **Post date:** [January 31, 2003, 6:18pm UTC](https://boards.straightdope.com/t/what-is-the-difference-between-a-worm-a-trojan-and-a-virus/151910/6 "2003-01-31T18:18:45Z")
Remind me never to send you to buy condoms… ---
**Author:** ![Ice\_Wolf](https://avatars.discourse-cdn.com/v4/letter/i/dfb087/32.png) [@Ice\_Wolf](https://boards.straightdope.com/u/Ice_Wolf)\ **Post date:** [January 31, 2003, 6:24pm UTC](https://boards.straightdope.com/t/what-is-the-difference-between-a-worm-a-trojan-and-a-virus/151910/7 "2003-01-31T18:24:15Z")
_sigh_ Well, at least _I_ tried to help you out seriously, **Docklands** … ---
**Author:** ![RealityChuck](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/realitychuck/32/195_2.png) [@RealityChuck](https://boards.straightdope.com/u/RealityChuck)\ **Post date:** [January 31, 2003, 6:29pm UTC](https://boards.straightdope.com/t/what-is-the-difference-between-a-worm-a-trojan-and-a-virus/151910/8 "2003-01-31T18:29:22Z")
Note that even internet security experts can’t keep the definitions of “worm” and “virus” straight. Often you’ll see something listed as a virus despite the fact it fits the definition of worm. ---
**Author:** ![Ethilrist](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ethilrist/32/4604_2.png) [@Ethilrist](https://boards.straightdope.com/u/Ethilrist)\ **Post date:** [January 31, 2003, 6:32pm UTC](https://boards.straightdope.com/t/what-is-the-difference-between-a-worm-a-trojan-and-a-virus/151910/9 "2003-01-31T18:32:02Z")
> [@](#): > > \*Originally posted by Ice Wolf \* > \*\*_sigh_ > Well, at least _I_ tried to help you out seriously, **Docklands** … \*\* See, my theory in GQ is that I try to steer clear of posts I don’t have the answer to, until somebody posts an actual informative answer, then I can jump in and post some sort of wiseass remark. Thanks for coming up with an answer! ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [January 31, 2003, 6:32pm UTC](https://boards.straightdope.com/t/what-is-the-difference-between-a-worm-a-trojan-and-a-virus/151910/10 "2003-01-31T18:32:36Z")
**Ice Wolf** ’s quote only tells part of the story. Suppose a jerk wrote and distributed a “special program”. It might look innocent, but when run did something bad. E.g., wiped your hard drive. Emailed info on your computer to the author, etc. That’s a trojan. You only get the trojan if you download the whole program and the trojan doesn’t make copies of itself. People copying the program cause the spread. A virus is a self-propagating program that needs to attach to another program to work. If you run a virus infected program, it looks for other programs to infect and copies itself. If the infected program is never run, the virus doesn’t propagate further. Many viruses spread nowadays thru email attachments. You “view” the email (which in poorly designed software runs the code in the attachment), the virus then looks for other addresses on your computer and mails itself to them. Note that a lot of email header forging goes on. Who sent you the virus and who is listed as sender can be two different people. A worm is completely self-propagating. It runs on its own. A worm spreads over networks by attacking ports on other computers, looking for vulnerable programs. Once found, it sends itself to the other computer, and then the new copy starts running and propagating. Note that some infectors are a mix of the above. 1. The Internet was swamped last Sat. by a very large worm event. 2. All news articles in standard media I read called it a “virus”. ergo 3. Never, ever trust what standard media says about tech. They are completely and utterly clueless.