Like the title says what are the rules. If I miraculously got a private key to a wallet that had Bitcoin in it but was not mine originally then does that mean I now own the wallet like finders keepers and is there any legality issues with this in the usa,uk,canada,south america. Is this more of a morality should you or should you not.
I will consider it morally wrong to have a wallet that is not yours under your control, especially if you have gotten the complete access to it. Come to think of it, you did not create the wallet and you did not get it as a gift. However you arrived at this wallet is really questionable or maybe a wrong exposure of private key details but don't collect what is not your just because it is available.
I mean, values are what guides people and not necessarily the money we all work day and nigh to earn. If your value system doesn't complain about you wanting to take what is not ideally yours then it needs to be checked.
If it is legally right or wrong depends on the government policy in your domicile country.