1. In a networked client-server computer system having a plurality of users of the client-server system and including software performing database queries via a DBMS for users of the system, a method of two-phase query security, the method comprising: receiving by the client system a query string from one of the plurality of users, the query string including references to database objects; transforming the received query string by the client system to an intermediate query string; performing a first phase query security by the client system including: identifying the referenced database objects; and inserting a security marker into the intermediate query string for each respective identified database object, thereby forming respective pairs of query parts and marker parts; transferring the intermediate query string, including the query parts and the marker parts, to the server system; performing access control checks by the server system on the inserted security markers in the intermediate query string; and replacing the inserted security markers with corresponding enforcing means to enforce access control.