Researchers from Nanyang Technological University (NTU) in Singapore say malicious apps on your phone could use the datastream from those sensors to build up information on how the phone is used and ultimately guess the phones PIN. The researchers algorithm was able to guess a PIN with a 99.5% accuracy on the first try using a list of the top 50 most common PINs, although the success rate went down to 83.7% when it tried to guess all 10,000 possible combinations of four-digit PINs within 20 tries.”]