Last year, the Department of Homeland Security launched a pilot project in Washington DC, deploying a network of sensors to ascertain the extent of cell phone surveillance being conducted in the capitol. They found that not only were International Mobile Subscriber Identity (IMSI) catchers in use, but some were being used in proximity to “potentially sensitive facilities like the White House.”

The revelation comes from a letter sent to Senator Ron Wyden of Oregon, a member of the Select Committee on Intelligence from Christopher C. Krebs, the Senior Official Performing the Duties of the Undersecretary for National Protection and Programs Directorate (NPPD), who was recently nominated to become the directorate’s Undersecretary. In his letter, Krebs notes that the test was to “better understand potential IMSI catcher activity” in the region, and that while the NPPD observed activity near the White House, it didn’t validate or attribute the activity to any “specific entities, devices, or purposes.” Some of this activity could have been from legitimate sources: he notes that US counterintelligence and law enforcement personnel followed up and “determined some detected signals were emanated from legitimate cell towers.” But this leaves the possibility that some of these signals were not from US authorities.

Krebs goes on to note that DHS has “received reports from third parties about the unauthorized use of IMSI catcher technology, as well as reports that nefarious actors may have exploited Signaling System Seven (SS7) vulnerabilities to target the communications of American citizens,” and that the DHS released a report last year outlining the potential threats that this technology posts to national security.

IMSI catchers — sometimes referred to as Stingrays — are devices spoof cell phone towers and can intercept phone communications and are tools that have been used by the US Marshals, the New York City Police Department, Immigration and Customs Enforcement, and even the Internal Revenue Service. Congressional committees have urged Congress to enact legislation to regulate their use.

The Washington Post notes that the DHS study helps validate what other researchers have suggested: that foreign intelligence services have used the technology to try and gather information on US officials. In a statement, Senator Wyden notes that he’s concerned that spies could be targeting President Donald Trump, other senior officials, and American citizens, and called on the FCC and Trump administration to do something about it.

Wyden also takes a jab at Trump’s own phone habits, saying that he’s set a poor example. Last year, senators had questioned the president’s use of an unsecured Samsung Android phone, while a recent report from Politico indicated that he continues to use a pair of iPhones — one to make calls, the other for Twitter — and has resisted requests to swap the Twitter phone out each month, “telling them it was ‘too inconvenient,’” and that he’s gone for as long as five months without security experts examining the phone.