Hundreds of Chinese-made drones have been detected in restricted sections of Washington, D.C. over the last few months. According to a report from Politico, the drones have geofencing built in to prevent them from flying where they’re not allowed, but the pilots are modifying them to get around the no-fly zone restrictions.

The drones are manufactured by the Chinese company DJI, the world’s largest personal and professional drone manufacturer whose products make up a majority of the recreational drones in the United States. 

Security experts are concerned about the company’s ties to the Chinese government. Chinese-made drones are banned by the Defense Department and the Interior Department only allows them in emergencies.

In fact, some national security agencies are concerned the Chinese-made drones could lead to a new form of foreign espionage. Three Senate committees – Homeland Security, Commerce and Intelligence – have received classified briefings on the matter. 

“Any technological product with origins in China or Chinese companies holds a real risk and potential of vulnerability that can be exploited both now and in a time of conflict,” Senate Intelligence Committee Vice Chair Marco Rubio, R-Fla., told Politico in an interview. “They’re manufactured in China or manufactured by a Chinese company, but they’ll put a sticker on it of some non-Chinese company that repackages it so you don’t even know that you’re buying it.”

Rubio expressed concern that technology can be exploited if it has vulnerabilities embedded into the software or hardware.

“These may be just innocent data collection — or really just looking around, seeing what’s happening — and not in a systemized way. But the potential, of course, is that eventually they could be more dangerous,” Rachel Stohl, of the Stimson Center, told Politico.

Although there is no evidence the drones are being controlled by the Chinese government, it is possible their high definition cameras or sensors could be hacked for intelligence gathering, according to the article.