Wow, that's an interesting situation, if I were you, I wouldn't rush to spend that money until I found out where it came from. There was a case when I received a bonus like that, and then it turned out that it was sent by mistake by an old acquaintance, try using the find a person by name feature on online search engines. This will help you find digital traces of this Mike's social media profiles or professional contacts, this way, you can figure out if it's someone from your past or a complete stranger. The search is anonymous, so you're not risking anything. It's better to check everything yourself than to wait for a call from the bank about a refund. Good luck with your investigation.