My account got jacked before too. Passwords taken, hats stolen, etc. Just submit a ticket. Explain what happened. Give any proof that you have on the hijacker. The process is pretty fast with steam.
Just make sure to run (ASAP):
- Malwarebytes Anti-malware (free-ware): http://www.malwarebytes.org/products/malwarebytes_free/
- SuperAntiSpyware (free-ware): http://www.superantispyware.com/
- If you use firefox, which I recommend. Install NoScript to block any java scripts from running without your permission. http://noscript.net/
[This stops you from clicking links that automatically install things without your permission.]
Once you are done doing all these things. Make sure to completely change all your passwords. What most-likely happened, is they installed a keylogger somewhere that takes periodic screenshots (in my case this was found in my apps folder, %APPDATA%). So they have all your information.
More information about my last incident with Yo_D (the hacker)-- http://www.sourceop.com/modules.php?name=Forums&file=viewtopic&t=30097&postdays=0&postorder=asc&start=900
and
Not sure if any of this will help you. But good luck flame.