1. A computer-implemented method performed by data processing apparatus, the method comprising: receiving security processing rules, each of the security processing rules defining one or more security checks and security operations corresponding to the security checks and that are to be performed when the security checks occur; and generating from the security processing rules a mapping of security checks to security operations, the mapping including a security check entry for each security check that is defined in one or more of the security processing rules, and each security check entry being mapped to one or more security operations that the security processing rules define as corresponding to the security check.