The personal information encoded in genomic DNA should not be made available to the public. With the increasing discoveries of new genes, it has become necessary to establish a security system for personal genome information. Although many security systems that are applied for electrical information in computers have been developed and established, there is no security system for information at DNA level. In this paper, we describe a new security system for information encoded within DNA. The original genomic DNA was mixed with many kinds of dummy DNAs (mixtures of natural and/or artificial DNAs) resulting in the masking of the original information. Using these dummy molecules, we succeeded to completely ?lock ?the original genome information. If this information must be ?unlocked ?, it can be extracted and analyzed by a removal of dummy DNAs using molecular tagging techniques or by selective amplification using key primers.