Part 15/19:
The security model relies on the assumption that a majority (more than 50%) of hashing power remains honest. An attacker would need to control a majority (known as a 51% attack) and produce more cumulative proof-of-work than the rest of the network combined—an extraordinarily costly endeavor, requiring billions in hardware and energy investments. The lecture underscores that, practically, the network’s decentralization and cumulative work make such attacks infeasible.