What is the legend of Trojan Horse?

It was a large horse made by the Trojan's of wood with a door concealed under the belly, it was offered as a gift to gain entrance into a fortrace, once the fortrace doors were opened and the large horse was brought inside, the soldier's inside waited til all was quit and gained access to fight inside the fortress. So a Trojan Horse is a term used for a hidden virus, It is concealed in a program and then gains access through disguise into your computer....