Nanjing University researchers have figured out a way to track smartphone users riding the subway.

The technique, which requires a malicious application to be introduced on the target's smartphone, involves using accelerometer readings to track where riders are getting on and off trains, according to a research paper released on Friday.

The researchers conducted real experiments on Nanjing Metro Line 2 in China. “The results show that the [average] inferring accuracy can reach about 70 [percent] and 90 [percent] when a volunteer rides the train for 4 stations and for 6 stations, respectively,” the paper said.

The attack can enable someone to identify a target's living and working areas, and is especially threatening because platforms such as Android allow applications to access the accelerometer without explicit consent, the paper noted.