This document discusses the security of cryptocurrencies. It begins by defining cryptocurrency and explaining how cryptocurrency transactions work using blockchain technology. It then discusses some of the key properties of cryptocurrencies like irreversibility, pseudonymity, and controlled supply. The document outlines some benefits of cryptocurrencies like lack of third party seizure and anonymity, but also challenges like high energy usage and possibility of lost wallets. It then discusses some specific security issues with blockchain like its complexity, size of the network, and traditional scams. It concludes by covering security issues with cryptocurrencies like spoofing payment information, errors in user addresses, and loss of wallet files.