University of Pennsylvania researchers tested the Google Nexus One and HTC G1, both of which use a graphical password system to unlock the phone that works by swiping a set pattern on the touchscreen.
Unlocking your phone in this way leaves oily residues on the screen that can remain even if you wipe it. "Latent smudges may be usable to infer recently and frequently touched areas of the screen -- a form of information leakage," warns the article.
Using standard cameras and lights, researchers took pictures of the touchscreens and analysed the images with simple photo-editing software available on most home computers.
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