An online interactive map showing the locations and activities of people who use fitness tracking devices - such as Fitbit - has raised security concerns for military personnel.
The Global Heat Map, published by the fitness tracking app Strava, uses satellite information to chart the movements of subscribers as they run or cycle, illuminating busy areas.
The map is not live but shows a pattern of accumulated activity between 2015 and September 2017.
It appears to include the movements of soldiers stationed at foreign military bases in countries like Afghanistan and Syria.
An Australian student, Nathan Ruser, first highlighted the issue when he came across the map while browsing a cartography blog last week.
The map shows a great deal of activity in the US and Europe, but in war zones and deserts in countries such as Iraq and Syria, it becomes almost entirely dark - except for scattered evidence of activity.
A closer look at those areas brings into focus the locations and outlines of well-known US military bases, as well as other lesser-known and potentially sensitive sites - possibly because American soldiers and other personnel are using fitness trackers as they move around.
Strava says it has 27 million users around the world.
The Global Heat Map was posted online in November 2017, but the information it contains was only publicised recently.
The data could provide information to someone who wants to attack or ambush troops, the Washington Post reported.
Strava said it had excluded activities marked as private from the map.
Military officials are looking into the situation to determine how to respond. Spokeswoman Major Audricia Harris said:
"The Department of Defence (DoD) takes matters like these very seriously and is reviewing the situation to determine if any additional training or guidance is required, and if any additional policy must be developed to ensure the continued safety of DoD personnel at home and abroad."