System and method for network security

A system and method analyzes queries in a computer network, and identifies problem-causing queries that could be harmful to the system. If a query does not match any queries in a database, the query is transmitted to its destination. If a query matches a query in the database, that query is blocked from transmission to the destination. If a query is transmitted to its destination, and it is later determined that query caused a problem on that destination, that query is added to the database of queries. In one embodiment, a query that does not cause any problems is written to a pool of current up-to-date backup databases that may be used if the main system goes down. In another embodiment, the system tests variants of a query that caused a problem at the destination to attempt to discover other queries that could cause a problem.