Most fires which break out inside computer centers are due to an electrical short circuit or the buildup of deposits of inflammable dust or waste, together with the presence of people smoking. One danger to computers comes from the mass of cables which are found in the false floor plenum because the covering on the cables burns easily. While the human nose is the best smoke detector, electronic smoke detectors should be used when people are not working. Three fire extinguishing systems are effective against fire: water, carbon dioxide, and bromotrifluormethane. Computer room personnel, the security guards, and the fire brigade can all be useful in intervening in potentially hazardous situations. Finally, emergency exists should be kept clear. Aggression, the other major problem in computer facilities, is carried out by three distinct groups--terrorists and political revolutionaries, anticomputer individuals, and unbalanced persons with a grudge against a certain organization who choose this method to display it. Finally, one person should be responsible for computer security and should draw up a comprehensive security plan. Elements of a security system are appended.