How phone apps track us in secret

It doesn't matter how many precautions you take to protect your privacy: if you are carrying a smartphone which is switched on, it is likely you are still being tracked.

More than 100 mobile phone apps secretly leak information about the user's battery power, which can be used to calculate their location with alarming precision, experts have claimed.

According to researchers at Stamford University, different mobile phone masts suck up users' battery power at different rates, making it possible to piece together someone's movement between so-called 'base stations'.

The technique is similar to the way police can locate suspects, by tracking their mobile phone signal as they move between base stations.

Anyone tracking that person would have to know the broad geographical area they were in, but once they had that information, they would be able to piece a map together.

“Applications that want access to location data can bypass all these restrictions and covertly learn the phone's location,” the researchers said.

“This can be done with no knowledge of the base stations to which the phone is attached, as long as the attacker knows the general area in which the victim moves.”

Many companies try to track mobile users' movements in order to target them with the adverts most likely to make them spend money.

For example, a coffee shop would be keen to send money-off vouchers to mobile phone users passing their doors, whilst a clothes retailer might want to send adverts to people in a shopping centre.

Many mobile phone users try to protect their privacy by turning off features like 'location services', designed to track their movements.

However, Peter Sommer, a digital forensics expert who has taught at London School of Economics, said: “If you use a mobile phone, you will be tracked.”