Last year a man in Canada was arrested for downloading child pornography onto his laptop, but he used someone else's wireless access point to access the illegal material. That same year federal officials accused a man from Michigan of conspiring to steal credit card numbers from the Lowe's chain of home improvement stores by taking advantage of an unsecured Wi-Fi network at a store in Detroit.

In the future, stealing secrets from unsecured networks may no longer be possible. Researchers at the University of Warwick have devised a method of producing tunable surfaces that can selectively block Wi-Fi signals from spilling out of the office.

Dr Christos Mias, in the University of Warwick's School of Engineering, has developed a "dipole grid-based frequency selective surface" to perform this task. This grid of circuitry has the potential to be embedded in any glass window and then tuned to block the selected frequency. The circuit can easily be tuned to block a different frequency if circumstances in the office change without having to remove the window or the circuits.

Mias has already worked with colleagues at other universities and institutions to produce non-tunable FSS configurations on standard domestic glass. Both optically transparent thin-film and opaque micro machined conductors have been employed attenuating the power of the incoming signal, at selected frequencies (above 20GHz) by 100 to 1000 times. ®

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