I am Ben and I am in forth grade. I would like to know what a trojan horse is.

Well Ben, I notice that you said "a trojan horse," rather than "the trojan horse." That does make a difference in the explanation. First I'll review (in case you didn't know) what the trojan horse was, then we'll talk about how that phrase is used today in the world of computers.

Did you ever learn about the Trojan War? The Trojans were citizens of the city of Troy. The story of their war with the Greeks is recounted in Homer's Iliad, and other Greek literature. According to the story, the Trojans defended their city against the Greeks, but they finally lost when their enemies built an enormous wooden horse and hid a group of soldiers inside it. The Trojans thought it was a peace offering, so they brought it into the city and had a big party.

Then, in the middle of the night, while everyone was asleep, the soldiers climbed out of the horse and opened the city gates, letting in the Greek army. The Trojans were defeated because they were so gullible.

That's the trojan horse. But today we use that phrase to mean something similar, but different.

In computer terms, a Trojan Horse is a computer virus that is designed to fool people, just like the Trojans were fooled. It may be a program that is supposed to do something helpful, but really is also doing some unhelpful things.

Maybe you get an email that says "The attached file is an update from Microsoft. Open it to update your computer." Only, it's not really an update from Microsoft - it's a program that deletes all the files on your computer. But you believe the message, so you open the file. Now you're just like the Trojans. You thought you had something nice, but it turns out to be very nasty instead.That's a Trojan Horse.

Or you might be looking for a piece of software to do a particular job. Maybe you want some photo editing software, or screen capture software, or video conversion software. So you go looking online, and you find a free version of the software. You get excited about not having to pay anything, and you download it. But you don't realize that the software is actually spying on you, or damaging your computer in some way.

And by the way, that should be a good reminder to you of how cautious you should be when you download files from the internet, and when you open files attached to e-mails. Don't be like the Trojans - always be suspicious!