On this day in 2002, our friend @adam3us formally released his groundbreaking paper, "Hashcash - A Denial of Service Counter-Measure." While its original purpose was to combat email spam, this simple yet powerful idea laid the intellectual foundation for something much bigger. Hashcash proposed a simple concept: require a small, but non-trivial, amount of computational work to be performed by a sender. This work would be easy for a single person to do but impossibly expensive for a spammer trying to send millions of emails. This very concept, a proof of computational work required to earn a privilege, was the elegant blueprint that Satoshi Nakamoto directly cited and used for #Bitcoin's mining algorithm. From an anti-spam measure to the bedrock of a global, decentralized monetary network, Hashcash is a testament to the power of foundational ideas. Happy Hashcash Anniversary to Adam Back, the pioneer who showed the world how to make spam and Sybil attacks expensive. 🙌🧡