If we're talking about finding Bitcoin private keys that contain balances (i.e. not any targetted attacks), that's a bit of a gray area and I don't think many countries would have laws specifying this.
It's not quite the same as trying to get access to someone's private account. You could say that it's the responsibility of everyone who participates in the Bitcoin network to know and accept all the risks. And if we create a situation where you're unable to use Bitcoin unless you're able to explain every transaction to authorities and prove that you're the "rightful" owner of the coins, then what would be the purpose of it anyway?