Someone is placing sophisticated espionage devices around the White House, and no one seems to know who.
The devices, known as IMSI catchers or Stingrays, trick mobile phones into thinking they're connected to a legitimate cell network and scoop up calls and text messages.
NPR reports the US Department of Homeland Security (DHS) has for the first time acknowledged it has "observed anomalous activity... that appears to be consistent with International Mobile Subscriber Identity (IMSI) catchers" around the White House and Capitol building in Washington DC.
But it doesn't know who's planting them, though it might be obvious why.
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DHS official Christopher Krebs said Stingrays' use "by malicious actors to track and monitor cellular users is unlawful and threatens the security of communications, resulting in safety, economic and privacy risks", CNN reports.
NPR says the devices are only legally allowed to be sold to law enforcement and public safety officials - not the general public.
But according to a Washington Post report, they can be built by "reasonably skilled hobbyists" for under US$1500.
Its reporter found 18 Stingrays in just two days by driving around the city - clustered around not just the White House and Capitol, but also foreign embassies and the headquarters of businesses that have contracts with the US government.
The DHS says it doesn't have the funding to pinpoint exactly where the spy devices are, or figure out who's operating them.