While computer systems can be quite susceptible to deception by attackers, deception by defenders has increasingly been investigated in recent years. Military history has classic examples of defensive deceptions, but not all tactics and strategies have analogies in cyberspace. Honeypots are the most important example today; they are decoy computer systems designed to encourage attacks to collect data about attack methods. We examine the opportunities for deception in honeypots, and then opportunities for deception in ordinary computer systems by tactics like fake information, false delays, false error messages, and identity deception. We conclude with possible strategic deceptions.