Most people working in cyber security recognize that the interconnections and complexities of our economy can have a huge effect on the destructiveness of cyber attacks. They refer casually to "network effects," "spillover effects" or "knock-on effects." Yet there is little understanding of how such effects actually work, what conditions are necessary to create them, or how to quantify their consequences. People working in cyber security also generally acknowledge that combinations of cyber attacks could be much more destructive than individual attacks. Yet there is little understanding of exactly why this is the case or what the principles would be for combining attacks to produce maximum destruction. These two sets of problems are actually the same. It is by taking account of the interconnections and complexities in our economy that cyber-attackers could devise combinations of attacks to cause greater destruction. To understand how this would work, we need to look at three features of our economy that are responsible for much of its structural complexity: redundancies, interdependencies, and near monopolies. Then, as we examine these features, we need to see how each of them would prompt a different sort of attack strategy.