I wrote (copy pasted / edited) a cheat for an online game that was in beta, when I was around 13. I released it (with no anti cheat protection), probably got a few thousand cheaters banned...

I then sold the cheat source code to a forum of cheaters, who integrated it into their own offering and paid me a small royalty. The source code was pretty much copy pasted from a guide with minimal changes to work on the correct memory addresses.