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Who's watching you? - Software thieves beware, your computer could turn you in

点击量:   时间:2017-11-09 06:01:03

By Mark Ward DETECTOR vans could soon be roaming the streets looking for companies that have not paid their software licence fees. Computer scientists at Cambridge have found a way to incorporate a clandestine signal into the radiation that computers normally emit. The message can be picked up and read up to 40 metres away. Markus Kuhn and Ross Anderson have found it is possible to display a hidden message—such as a software licence number—on a computer screen that can be decoded and read remotely on a modified television screen. To create the message, Kuhn and Anderson exploit the insensitivity of the human eye. This insensitivity is already used to make screen colours look richer than they are. A technique called “dithering” intersperses pixels of different colours to create shades that would not otherwise be possible on computers that can display only a limited number of colours. Kuhn and Anderson have developed software that, by changing a few black and white pixels, creates characters that look normal on screen but can conceal another letter. Kuhn says that many parts of a desktop monitor or a laptop screen radiate signals that a detector can pick up. The emissions may come from the screen, the driver cable for a laptop screen or even the power cables in the computer. A modified television set with a decoder can tune into these emissions and read them. Kuhn says that it is easiest to tune into the images in the 100 to 200 megahertz range, a figure that is related to the frequency at which pixels are drawn on the computer screen. Even the signals from low emission monitors can be read up to 40 metres away, although detection distances vary depending on the amount of noise from other computers in the office. But Kuhn adds that even in an office full of computers, image processing techniques should make it possible to pick out the licence numbers of all the software being used. Kuhn says their software could easily be modified to broadcast licence numbers, making it much easier for companies to monitor who is using their products. Kuhn says that Microsoft turned it down the chance to use this software: “They were worried about the public relations problems with this technology,” he says. The researchers have also come up with a way to thwart any attempt by your computer to broadcast your secrets. They have developed software that reduces the contrast of the display, so that even if software tries to create a hidden message,