Touchscreens became the dominant input device for smartphones. Users' touch behaviour has been widely studied in lab studies with a relative low number of participants. In contrast, we published a game in the Android Market that records the touch behaviour when executing a controlled task to collect large amounts of touch events. Players' task is to simply touch circles appearing on the screen. Data from 91,731 installations has been collected and players produced 120,626,225 touch events. We determined the error rates for different target sizes and screen locations. The amount of data enabled us to show that touch positions are systematically skewed. A compensation function that shifts the users' touches to reduce the amount of errors is derived from the data and evaluated by publishing an update of the game. The independent-measures experiment with data from 12,201 installations and 15,326,444 touch events shows that the function reduces the error rate by 7.79%. We argue that such a compensation function could improve the touch performance of virtually every smartphone user.