The FBI has confirmed it is using shell companies to fly surveillance aircraft with cellphone scanners and video cameras over US cities on a daily basis – and without the need for warrants.

The aircraft were spotted over Baltimore last month monitoring the protests and riots in that city. An AP investigation has confirmed that these missions are the norm, not the exception. In the last month the newswire has tracked more than 100 flights in 11 states, including Houston, Phoenix, Seattle, Chicago, Boston, Minneapolis, and Southern California.

"The FBI's aviation program is not secret," Feds spokesman Christopher Allen said in a statement. "Specific aircraft and their capabilities are protected for operational security purposes," adding that the aircraft, usually Cessna 182T Skylanes "are not equipped, designed or used for bulk collection activities or mass surveillance."

Back in November reports surfaced that US marshals had flown aircraft fitted with mobile phone tracking systems, nicknamed dirtboxes after the Boeing subsidiary Digital Receiver Technology that provides the equipment.

Those aircraft can mimic legitimate cellphone towers, and log and track unique IMEI numbers broadcast by mobile devices within reach. The device's actual location can be determined by triangulation of the signal, and people identified through their handsets' IMEI.

The FBI flights appear to be mostly for carrying out video surveillance, however a significant number are thought to carry cellphone-snooping technology. The FBI has been careful to avoid mentioning this in court cases, and has not applied for warrants for the flights after getting clearance from the Department of Justice.

"These are not your grandparents' surveillance aircraft," said Jay Stanley, a senior policy analyst with the American Civil Liberties Union. "If the federal government is maintaining a fleet of aircraft whose purpose is to circle over American cities, especially with the technology we know can be attached to those aircraft."

The aircraft aren't directly run by the agency, but are owned and operated through a series of shell companies such as FVX Research, KQM Aviation, NBR Aviation and PXW Services. Most used the name Robert Lindley in the documentation, and the individual appears to have three different signature styles on documents.

The FBI declined to say if Lindley was an employee, and asked AP not to reveal any details of the shell companies, since setting up new ones would cost taxpayer dollars and remove the anonymity of the flights. AP declined to comply with the request after finding the company names in public documents. ®