1. A security client using a one-time execution code in an environment in which a server and a client are connected through a network, wherein the security client receives the one-time execution code from the server, loads the one-time execution code on a code container allocated to a memory area of a client program that is currently executed, executes the loaded one-time execution code, transmits the execution result to the server, and deletes the one-time execution code from the memory.