This talk will review some of the most spectacular security failures in blockchain systems, and will help you mitigate your risks. We will notably review some of the most dramatic Ethereum smart contract issues, discuss objectively the case of Iota's custom crypto, describe how we could have stolen $millions worth of tokens (but didn't), and present examples of bugs that we found in popular Bitcoin software utilities. In the second part of the talk, we'll review the different types of wallets and their pros and cons, and we'll discuss the risks and benefits of hardware-based wallets for individuals, organizations, and trading platforms. The speaker has an extensive experience auditing blockchain systems for leading cryptocurrencies, and now helps secure a cryptocurrency exchange platform.