Cryptography can increase the security of computers and modern telecommunication systems.
Software viruses and hardware trapdoors are aspects of computer security. Based on a combination of these two aspects, an attack on computer security is presented. The complexity of finding such an attack is discussed. This research started while the author was aangesteld navorser NFWO at the Katholieke Universiteit Leuven LNCS 0263, p. 459 ff.