A behavior blocker is a program that contain a list of rules that a legitimate program must follow. If the program breaks one of the rules, the behavior blockers alert the user. The “sandbox” concept is that untrusted code is first checked for improper behavior. If none is found, it can be run in a restricted environment, where dynamic checks are performed on each potentially dangerous action before it is permitted to take effect. By adding multiple layers of reviews and checks to the execution process, behavior blockers can prevent malicious code from performing undesirable actions.