Earlier this year, someone at the United States Department of Justice smuggled sensitive financial data out of the agency by embedding the data in several image files. Defeating this exfiltration method, called steganography, has proved particularly tricky, but one engineering student has come up with a way to make espionage work against itself. Keith Bertolino, founder of digital forensics start-up E.R. Forensics, based in West Nyack, N.Y., developed a new way of disrupting steganography last year while finishing his electrical engineering degree at Northeastern University, in Boston. Steganography uses innocuous documents, usually an image file, as carriers for secret messages. Unlike encryption, steganography encodes the message while at the same time concealing the fact that a message is being sent at all. The Greek-derived name means “covered writing.”