This question already has an answer here:

I would like to know what a trojan looks like.

There was a great example of a worm (although it is old) posted by Wired. Viruses embed themselves into an existing program, by changing the existing code (if I am not mistaken).

On the other hand, I have no idea what trojans look like. Are they for example an executable file, which installs the desired software but also adds a backdoor?

Edit: I just posted another question, where I tried to specify what exactly I would like to know. Sorry for the "spam" and confusion.

marked as duplicate by WhiteWinterWolf, Anders, Xander, Matthew, Mike Ounsworth Jun 17 '16 at 21:59

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.


In the IT world a trojan horse is a file wich looks like for instance an MP3 file but is actually malicious. When you open the file you install the malware. So actually you do all the work and install the file by yourself by running an .exe file wich looks like an MP3 file.

Most of the time this is done with some great social engineering tricks but also torrent sites a crowded with trojans.

So how do we protect ourselves? Well it is quite simple in theory but in practise it seems a lot more difficult:

  • Don't open any attachements in your email from unknown senders (this is one of the most made mistake)
  • Scan every file you download from a site or friend you are not familiair with. Just right click and press scan.(scanning all files is always better but users tend to be lazy)

If you ever find your computer has been infected with a Trojan, you should disconnect your Internet connection and remove the files in question with an antivirus program or by reinstalling your operating system.

for some more read I recommend this article.

Quick side note: I used MP3 as an example, in e-mails it is most of the time a PDF for example but it can embed itself in anything

  • Thanks, just a quick sub-questions, Does it necessarily have to be an .exe file? – DrDoom Jun 17 '16 at 7:53
  • It is a .exe file hidden in a decoy extension. – Bomskie Jun 17 '16 at 7:55
  • Flagging as non-answer. 95% of this post does not explain how a computer trojan is built, which was the question, the remaining 5% is from mythology. – techraf Jun 17 '16 at 8:01
  • I think you have to read the question again, The question was: What does it look like. Not how it is build – Bomskie Jun 17 '16 at 8:02
  • I am happy with the answer. If I will have any more in depth questions, I'll just ask/make another question. Although the mythological part was a bit redundant, since if you google trojan horse malware it always gives you the mythological part 1st, and believe it or not I did google it 1st before posing the question =) – DrDoom Jun 17 '16 at 8:08

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