A method, system and program are provided for determining if a system clock has been reset backwards in time by using a randomly generated set of bytes (such as a randomly generated or type 4 UUID) as a time epoch. By generating a time epoch at boot time and whenever the system clock is set back in time, an application can compare the time epoch value at an earlier point in its execution, with the current time epoch. If the time epoch values are different, the application will know that the system clock has been set back in time.