"Monitors, CRT's, screens, cathode ray tubes, whatever you want to call them. The inside of most monitors is just like televi- sion sets. There is an electron beam that writes to the surface of the screen, the phosphor coated one. That's what makes the picture." "That's how a TV works? I always wondered." Duncan was only half kidding. "So, the phosphor coating gets hit with a strong electron beam, full of high voltage energy, and the phosphor glows, just for a few milliseconds. Then, the beam comes around again and either turns it on or leaves it off, depending upon what the picture is supposed to show. Make sense?" "That's why you can go frame to frame on a VCR, isn't it? Every second there are actually lots of still pictures that change so quickly that the eye is fooled into thinking it's watching mo- tion. Really, it's a whole set of photographed being flipped through quickly." Duncan picked up the essentials on the first pass. Scott was visibly impressed. "Bingo! So this beam is directed around the surface of the screen about 60 times every second." "What moves the beam?" Duncan was following closely. "You are one perceptive pain in the butt, aren't you? You nailed it right on the head." Scott enjoyed working with bright stu- dents. Duncan's smile made his pudgy face appear larger than it was. "Inside the monitor are what is called deflection coils. Deflection coils are magnets that tell the beam where to strike the screen's surface. One magnet moves the beam horizontally across the screen from left to right, and the other magnet, the vertical one, moves the beam from the top to the bottom. Same way as in a TV." Scott paused for a moment. He had given simi- lar descriptions before, and he found it useful to let is audi- ence have time to create a mental image. "Sure, that makes sense. So what about this radiation?" Duncan impatiently asked. He wanted to understand the full picture. "Well, magnets concentrate lots of electrical energy in a small place, so they create more intense, or stronger magnetic fields. Electromagnetic radiation if you will. In this case, the radia- tion from a computer monitor is called Van Eck radiation, named after the Dutch electrical engineer who described the phenomena." Scott sounded pleased with his Radiation 101 course brief. Tyrone wasn't satisfied though. "So how does that explain the blackmail and the infamous papers you have? And why do I care? I don't get it." The confused look on Tyrone's face told Scott he hadn't successfully tutored his FBI friend. "It's just like a radio station. A computer monitor puts out a distinctive pattern of radio waves from the coils and pixel radiations from the screen itself, at a comparatively high power. So, with a little radio tuner, you can pick up the signals on the computer screen and read them for yourself. It's the equivalent of eavesdropping on a computer."