A global map showing the distribution of people using personal fitness devices risks giving away troop movements and secret military facilities around the world, according to defence analysts who have already used it to pinpoint bases in Afghanistan and the Middle East.

The American satellite navigation service Strava last year launched its Global Heat Map, a visualisation of user data showing the location of its 27 million subscribers including owners of Fitbit, Jawbone and Vitofit fitness monitors.

Swaths of the United States and Europe show up as a blaze of colour, indicating the millions of users.

However, the map goes dark across war zones – such as Syria and Iraq – except for tiny pinpricks of light apparently showing US military personnel or international troops wearing the devices. The revelation has set off a hunt for previously unknown black sites around the world.

A spokesman for US Central Command, told The Washington Post the American military was looking into the implications of the map.