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Greasy fingerprints can take the shine off a new touchscreen handset, and the smudges they leave behind could also leave it open to hacking, according to researchers.

When touchscreen devices are held up to the face, they pick up oil from the skin, explained researchers from the University of Pennsylvania at the Usenix security conference. The next time the password is entered, the pattern can be traced – and photographed – in the resulting smudges.