One of the most pernicious phrases in the debate over how to counter extremist use of social media is "whack-a-mole." br br In national security circles, many believe that suspending social media accounts used by violent extremists is a pointless endeavor. They argue that, as in the children's arcade game "Whac-a-Mole," suspending accounts is a fruitless endeavor because, they claim, new accounts are created for every account that is suspended. br br To examine this assumption, technologist Jonathon Morgan and I collected data on millions of Twitter accounts, including tens of thousands used by ISIS supporters, and found substantial evidence to the contrary.