According to the rapid growth of computer and internet recently, A hacking to steal infonnations and the computer vinls to destroy the data in computer are now prevailing in the whole world. A study of methods to protect the data of computer is in progress. One of the study is constmction of computer immune system using biological immune system tbat has ability of removal and protection from extemal invasion. In this paper, we make a change detection algorithm which is based on ability of distinction between self and nonself in T-cytotoxic cell that is one of biological immune cell. In algorithm, MHC receptors are composed of a part of self-file that is recognized as itself and those shall distinguish self-file from the changed file. As a result of applying this algorithm to the changed self-files, we prove the efficacy of detection of the self-files changed by computer virus and hacking.