It's also possible that Poloniex is run by people who would be politically opposed to involving the state in what they might see as their personal affairs too. I have no idea if that's the case and have no personal information either way related to Poloniex and their political views. It's just that it wouldn't be unheard of for someone in this community to be morally opposed to state involvement.

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And then there is the other scenario that they might feel a minor (D?)DoS attack simply might not be worth pursuing or involving the state. Where as they would otherwise if it was a more serious attack, or theft.