According to the disclosures, the U.S. Marshals Service program operates Cessna aircraft, from five metropolitan airports, equipped with a device which can mimic a cellphone tower and trick phones into reporting their unique registration information.

During a single flight, the dragnet data collection will scoop up identifying information and general location of thousands of cellphones, according to the Wall Street Journal.

Cellphones are programmed to connect automatically to the strongest cell tower signal. The device or "dirtbox" used by the Marshals Service mimics the closest and strongest signal. The phone cuts out phone companies as an intermediary. The method is used to target a cellphone being used by a person under investigation by the government agency -- a fugitive or drug dealer -- but in locating the one or two people, thousands of others are included.

U.S. police departments are increasingly using International Mobile Subscriber Identity Catchers (IMSIs) -- Stingrays -- from cars which intercept or capture the contents of phone calls, text, messages or Internet activity. A report by the American Civil Liberties Union North California showed that while use of surveillance tools was widespread in police departments, the public or even local makers were in the dark about most of their use. The Justice Department's program, however, is airborne and can collect a greater volume of information.

People with knowledge of the program wouldn't say how often the flights happen, but they are regular, and have a flying range covering most of the U.S. population.

The Justice Department would neither confirm nor deny the existence of the program and told the Wall Street Journal "discussion of such matters would allow criminal suspects or foreign powers to determine U.S. surveillance capabilities. Justice Department agencies comply with federal law, including by seeking court approval."

The program is the latest disclosure of surveillance on the American people within the U.S. without their knowing.

"[It's] a dragnet surveillance program," Christopher Soghoian, chief technologist of the American Civil Liberties Union told the Wall Street Journal. "It's inexcusable and it's likely -- to the extent judges are authorizing it -- [that] they have no idea of the scale of it." Within the Marshals Service, people told the Wall Street Journal, some have questioned the legality of such operations and the internal safeguards. It is unclear how the Justice Department oversees the program, and whether the existence of this program is known by the telecom companies who devices are being redirected by the program.

A Verizon spokesman told the Wall Street Journal the company was unaware of the program. "The security of Verizon's network and our customers' privacy are top priorities," said the spokesman. "However, to be clear, the equipment referenced in the article is not Verizon's and is not part of our network."