ata and decode it. Contrarily, the theory also provides guidelines for how an adversary would disrupt the hidden information. The theory is a fundamental and broad-reaching advance in information and communication systems that eventually will be imple- mented in commerce and numerous homeland security applications-from detecting forgery to intercepting and interpreting messages sent between terrorists. Using elements of game, communication, and optimization theories, Jody O'Sullivan, professor of electrical engineering at Washington University in St. Louis, and his former graduate student, Pierre Moulin, now at the University of Illinois, have determined the fundamental limits on the amount of infor- mation that can be reliably hidden in a broad class of data or information- hiding problems, whether they are in visual, audio, or print media. "This is the fundamental theorem of data hiding," O'Sullivan says. "One hundred years from now, if someone's trying to embed information in something else, they'll never be able to hide more than is determined by our theory. This is a con- stant. You basically plug in the parameters of the problem you are working and the theory predicts the limits." Data, or information, hiding is an emerging area that encompasses such applications as copyright protection for digital media, watermarking, finger- printing, steganography, and data embedding. Watermarking is a means of authenticating intellectual property-such as a photographer's picture or a Disney movie, by making imperceptible digital notations in the media identi- fying the owner. Steganography is the embedding of hidden messages in other messages. Data hiding has engaged the minds of the nation's top academics over the past seven years, but it has also caught the fancy of the truly evil. In February 2001, nine months before 9/11, USA Today reported that Osama bin Laden and his operatives were using steganography to send messages back and forth. THE UNBLINKING EYE-SECURITY AND SURVEILLANCE "The limit to how much data can be 