What are some notable scams in history that went unnoticed for so long?

NGL, I've been on both ends: had a good friend give me 13 BTC when they were less than $0.10 apiece, and I've no idea what happened to them. On the other hand, I may've also sold near the ATH of 2017 and taken my entire family on a no-expense-spared Christmas trip fully paid by said profits. Still... 13 BTC at that latter moment would've been worth near a quarter mil. 🥹🤷🏼‍♂️