what do you mean you closed your browser... do you think maybe someone accessed it and found that mt gox was already logged in and stole it?
this seems most likely...
I meant - there was CSRF vulnerability on mtgox.com. In order to exploit it - I had to have active session and visit some site with exploit. But I shutdown laptop and did not visit any websites. So CSRF is not my case. Looks like some one got hands on their DB with all balances and passwords etc.