Is Bitcoin Secure?

In this video, we discuss the security of the bitcoin blockchain. We assume that you are familiar with basic terminology such as transactions, blocks, and mining. First we discuss so-called 51% attacks on blockchains. Then we discuss whether it might be profitable to be dishonest. This and other tricks show that it is not trivial to understand whether a blockchain is actually secure, because we first have to understand whether following the rules is the best strategy.