Even if a virus invades a program in operation according to the present invention, regardless of the timing and means of invasion and the number of attempts thereof, the present program autonomously and unassistedly detects the virus as contamination of a memory area used by the program and disinfects the contamination for quick recovery in order to continue the normal operation. The present program detects the virus as contamination caused by false information against the intent of the present program. Upon occurrence of contamination, the present program detects the contamination as a predicate inconsistency. However, this scheme is not for detecting an invading virus but is needed as a structural requirement in order for the program to exist as a legitimate program. The present program disinfects the detected contamination using a scheme in accordance with the present invention. The timing of disinfection prevents the symptoms of the invading virus from appearing, in view of which this exerts the same operational effect as that of destroying the viral intention. Consequently, the virus invading the present program is disabled by the present program before appearance of the intended symptoms of the virus.