1. A method performed by one or more data processing apparatus, the method comprising: identifying a data movement rule associated with a set of one or more computers, the data movement rule including one or more criteria identifying restricted data movement, and one or more actions to take when a computer from the set of computers violates the data movement rule, the one or more criteria associated with the data movement rule including a data movement threshold specifying an amount of data; detecting a data movement associated with a computer from the set of computers, the data movement including data being transferred from the computer to a destination, wherein at least part of the detecting occurs during the data movement; determining that the detected data movement violates the data movement rule based at least in part on an amount of data associated with the detected data movement exceeding the data movement threshold associated with the data movement rule; and performing the one or more actions associated with the data movement rule upon determining that the data movement violates the data movement rule.