The accused spies posted the seemingly mundane photos on publicly accessible websites, but then extracted coded messages from the computer data of the pictures, according to the criminal complaint filed by the FBI. Although computer scientists have theorized about the existence of this communication technique for over a decade, this is the first publicly acknowledged use of the technique.
"There have been occasional claims in the press about al Qaeda using it, but never with any evidence or even attributed to specific government officials," said Steven Bellovin, a professor in the Columbia University department of computer science. "Here, we have court papers filed by the FBI under penalty of perjury that says these folks were doing it. The threat, in other words, is no longer hypothetical."