Trojan horses are not self-replicating like viruses so they are not spread inadvertently. If someone gives you a trojan horse it is likely to be a malevolent act. Logic Bombs Logic bombs are pieces of code hidden within a program which trigger when some specified act occurs. An old and common example is where a programmer will make the accounting system stop operating if their name is not on the payroll. Other logic bombs can be more destructive.
Logic bombs are misnamed - a better analogy is a landmine.
As the world develops virus paranoia, it is no longer necessary to send a virus to shut down a system. The threat of a virus is often enough. As well as the AOL4FREE trojan horse, there was the AOL4FREE virus hoax. This hoax said that if you opened an email message with AOL4FREE in its subject line, your hard disk would be erased. When this hoax reached UC, many people shut down their email disrupting internal communication.