To aim to provide a monitoring system and a program execution apparatus that are capable of maintaining the security intensity even in the case where an unauthentic install module is invalidated. Install modules included in an apparatus each monitor an install module, which is a monitoring target indicated by a monitoring pattern included therein, as to whether the install module performs malicious operations. An install module that performs malicious operations is invalidated in accordance with an instruction from an update server. The monitoring patterns are restructured by the update server such that the install modules except the invalidated install module are each monitored by at least another one of the install modules. The restructured monitoring patterns are distributed to the install modules except the invalidated install module.