2 Answers

A trojan virus is one that you unwittingly download onto your machine because it can pass through real time scanning software discuised as a harmless program.

It isn't really dangerous until it executes. It usually executes by the operator clicking on it, but it can also auto execute if you don't have the latest Windows patches. Always use the latest browser version and updates.

It can also simply be a program that downloads viruses from servers while you're online.

The word Trojan includes many types of viruses now, but the original idea was a virus that could sit in the temperary internet files or just somewhere on your system until something set it off like you clicking on it.

it''s a giant horse