There is a new virus going around in Steam here is how it works in general.
You get a message from a friend questioning something about you like, WTF dude? or will you change that? following a link that contains the word screenshot. you are better off not clicking that link since it will make you download a file that sends your account information to the hacker, who then apparently steals stuff out of your steam inventory and game inventories by using your account to trade, later on if you aren't fast enough the virus will apparently make you post the same to your friends in Steam.
So again, no clicky the linky.
I was informed about this by Sligwolf because it happened to a friend of his and he got the link but he didn't click on it. As far as i know Shadowz was so unlucky to click it.
Stay Safe , this is meant as a little warning and precaution