virus
Ask three IT people how to defend yourself from viruses and you will get four answers ... so here's a fifth!
A virus, generally speaking, is an obnoxious bit of software written by an equally obnoxious adolescent that hasn't discovered girls yet! That's cleared up the technical bits, so how do you get one? It's quite difficult to get a virus these days, everybody and their uncle now writes anti-virus software. Some, like the very good AVG from Grisoft are free to non commercial users. Outlook now blocks all dangerous attachments so there is no excuse.