In the last days of the election season, vast swaths of the internet shut down in the United States. It was the result of a DDoS attack on a single company, Dyn, that manages a large part of the internet’s infrastructure. A DDoS attack can be brutal and difficult to stop, because it deploys bots implanted in vast numbers of hacked machines to hammer servers with database calls, too many to sustain. The result is a crash. This one affected everyone’s favorite websites.