It could be any number of things as far as I can tell.
what?
Are we talking "whoops gave out my pass darn" hacking or "Beep beep account decrypted code 101010010010110" hacking? Either way, that really sucks. Contact steam support, see what they can do.
im going to continue to contact them, haven't yet. i saw the email while making a support account.
also, ive never given my password out and never will.
and im sure it was xxxxkill because he "never gets presents or games", so i could see why his greediness could lead to hacking my account he envied for.