When I was a kid I used to play this online game called virtualpups. It was basically just buying and breeding virtual dogs. Every new account gets 50k in-game cash, which can be transferred between accounts.

I spent weeks "hacking" literally tens and tens of accounts by guessing usernames and passwords (stuff like 12345) and took all their cash, and also made probably well over 100 secondary accounts of my own for the 50k startup money. I was literally a millionaire in that game and idk how it wasn't suspect enough to be investigated because I wasn't offering any services.

It's definitely the most ethically wrong thing I've ever done, and I was only 8 or 9 whilst doing it.