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Is a worm a virus? Do all trojans carry backdoors? Is the Internet making a mockery of the English language?

Virus vocabulary

In the frontier world of the Internet, people often use the same word to mean different things. So here goes with an attempt at definitions:

Virus - a program that infects your computer against your wishes, often, though not always, with harmful results.

Worm - a self-replicating virus. Some (technical) people would argue that worms are not a kind of virus, they're an entirely separate category, because viruses cannot self-replicate. This distinction is already lost on most people and looks likely to get more fudged as time goes on. In common use, worms are a sub-category of viruses.

Back door - there are two nuances of this expression, but they're very similar. A back door in a program is a sneaky way in that's been left there on purpose by the programmer, so they can get access whenever they feel like it. There are rumours that some encryption programs have back doors so the security services can easily decrypt everything.

A back door program, on the other hand (sometimes written as one word - backdoor), is a hacking tool that takes control of the victim's computer. It's a sneaky method of entry for a hacker.

There are two elements to backdoor software. The "client" program, which must be installed on the victim's computer, and the remote control, which stays on the hacker's machine. Sometimes when people refer to a backdoor program they mean both elements, and sometimes they mean just the client element.

Trojan horse - a program that may appear benign but carries a hidden, dangerous payload, just like the wooden horse of Greek mythology. So what looks like an innocent game or animation may carry a bit of code that gives a hacker control over your computer.

Often the word horse is dropped and they're just called trojans (or Trojans). Many times people talk of trojans when really they're referring to the client element of backdoor code rather than the carrying mechanism. That's no big deal, but it can get messy because trojans don't always carry backdoor code, they sometimes carry plain old viruses. (Or should that be worms? I give up.)


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