A rule engine configured with at least one hash table which summarizes the rules managed by the engine. The rule engine receives rules and automatically adjusts the hash table in order to relate to added rules and/or in order to remove cancelled rules. The adjustment may be performed while the rule engine is filtering packets, without stopping. The rules may be grouped into a plurality of rule types and for each rule type the rule engine performs one or more accesses to at least one hash table to determine whether any of the rules of that type match the packet. In some embodiments, the rule engine may automatically select the rule types responsive to a set of rules provided to the rule engine and adapt its operation to the specific rules it is currently handling, while not spending resources on checking rule types not currently used.