The Sitok upgrade was an advanced security and diagnostic program developed by the Vulcan computer scientist Sitok in the 2350s. The Sitok upgrade was applied to most Federation and Starfleet computer systems during this period; however, for some older computer systems, the Sitok upgrade caused major system crashes. In most such cases, a facility's computer hardware was upgraded to accommodate the Sitok upgrade; a notable exception was Avril Station, where it was determined that the costs of the upgrade outweighed its benefits. (SCE eBook: Security)