Get "Jade" (http://psteamcommunity.yuanyoumao.com/profiles/76561198106467649/) Banned!

was playing TF2 and I get logged out. I think it was a mistake but then when I get logged back in, I have a new Friend. A player "Jade" (http://psteamcommunity.yuanyoumao.com/profiles/76561198106467649/) Some how got on my friends list. I go to my TF2 inventory and I was missing all my valuable items *POOF*! I go to my trading history and my Trade offer history. I find that "Jade" sent a trade offer showing jade offering nothing for all my valuable TF2 Items. It shows I accepted the trade offer, Though I never did (This is my history http://psteamcommunity.yuanyoumao.com/profiles/76561198051130353/tradeoffers/?history=1) Sadly I cant get a screenshot. I look on my phone to see I got a email that I got logged on to a new computer on the IP: 46.176.124.79. How did this "jade" get past Steam Guard, Steam Guard prevents trading on new computers? Please respond! I lost all my work I spent on TF2! Anything will Help!