The US says the military will be monitored by the findings, as a senator warns that the trade is a ‘national security threat’.

The United States Department of Defense has confirmed that adversaries are tracking and monitoring soldiers serving in the military using commercial location data, the latest demonstration of how information collected from phones and computers can be misused to track and trace people.

In letter shared with Sen. Ron Wyden and TechCrunch, the US Central Command said it is aware of actors who use purchased sites to target US personnel.

“USCENTCOM has received several threat reports regarding the use of adversary data to monitor or track US personnel in theaters,” the letter said.

The letter did not provide examples or explanations, and a Defense Ministry spokesman did not return a request for comment.

Reuters first report news on Thursday.

Location data is often collected from phones and computers through online advertising, which is purchased by data brokers, who sell the content on the market. Governments and militaries, including the United States, have purchased these in the past without obtaining a permit. In recent years, the FBI has done it warned consumers using ad blocking as a way to limit the amount of data that apps, websites, and other programs may collect.

Wyden told Reuters it was time to “start looking at the adtech industry as a national security threat.”