Perhaps the next killer apps, or market for hackers, will be altering your personal data. Phone rocker is a new begining.

People always finding a way to beat the system. Ha.Ha. I bet you a 'overweight' person thought of this. I can picture that person on the sofa eating chips and beer watching t.v. while the 'rocker' is doing all the steps. Ha.Ha.

Or some skinny person, who doesn't eat or exercise.

The answer to this is Big Data. Step counting is only one part of the data. If you combine this with location data you will see that the person does not move. You might think about given your step counter to somebody else but then you will find overlapping location data. The location data tells as well that you passed a CCTV camera but that camera does not have the picture of you. Meanwhile your electronic payment system knows that you spend money on baijiu and cigarettes and always eat in the local greasy spoon. Meanwhile you health insurance refuses to pay out but sues you for insurance fraud.

Most likely the earlier.