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If that is so, this seems way more like an bug/honest mistake from someone automatically/manually placing the 500$ into your wallet using the bitcoin blockchain but then the system fucked up and didn't credit you anything.
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I was wrong. The deposit address was the attacker address and was not actually an official deposit address linked to the users. The funds are not actually in freebitco.in's hands. It was not a simple/weird bug. The website was hacked either by a third party or an inside job.