Concerns have been raised that Nike's iPod runners kit could be used as a tracking device. 

Researchers at the University of Washington have revealed that it would be relatively simple to use the device to track its wearer.

"It is easy to track someone who has an active Nike+iPod kit sensor in their shoe," said scientists from the University of Washington's Department of Computer Science and Engineering, in a research paper.

"As part of our research, we built a number of surveillance tools that malicious individuals could use to track Nike+iPod Sport Kit owners.

"Our tools can track the owners while they our working out or just casually walking around town, a parking lot or a college campus. The tracked individuals don't even need to have their iPods with them."

The Nike iPod kit comprises a sensor placed in a shoe and a receiver which plugs into the bottom of the iPod Nano.

The sensor in the shoe detects when the wearer takes steps and transmits this information to the receiver.

"When you start a workout session with the iPod, software on the iPod collects the data from the sensor and keeps track of the distance you've walked and the pace at which you're walking," said the team.

"During a workout the iPod can provide audio feedback about the time, distance, pace or calories burned."

Once a workout is completed users can sync their iPods with iTunes and upload their data to the Nike+ website which contains software to track workouts, challenge other users to competitions and set personal goals.

"When you walk or run the Nike+iPod sensor in your shoe will transmit messages using a wireless radio. These messages contain a unique identifier that can be detected from 60 feet away," warned the researchers.

Owners of the kit are strongly advised to turn off the sensor when it is not being used in order to protect their privacy.

"Unfortunately, this suggestion will only help you when you're not working out. If you want to workout with the Nike+iPod kit, then we are unaware of any way to improve your location privacy during your workout," the group warned.