Britain's largest police force is using covert surveillance technology that can shut off mobile phones and intercept communications, according to a report in The Guardian.

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The article says that the London Metropolitan Police Service bought the technology, which acts like a fake cell tower, from a U.K.-based company called Datong plc. The suitcase-sized receiver reportedly tricks cell phones into thinking they are communicating on a regular cellular network, and this allows authorities to intercept text messages, data, and phone calls. Authorities can also track users within range of the fake cell phone network, the report says. It can also shut off cell phone service, a function designed so that authorities can disable a cell phone, which could be used to detonate a bomb.

The receiver is portable and can either be set up in a fixed location to pick up data in a particular area or it can be set up in a car and used to track individuals on the go.

Datong sells its technology to more than 40 governments around the world, including some in Eastern Europe, South America, the Middle East and Asia Pacific, The Guardian reports.

The article also states that between 2004 and 2009, Datong won more than $1.6 in contracts with U.S. government agencies, including the Secret Service, Special Operations Command, and the Bureau of Immigration and Customs Enforcement.

George Ogilvie, a spokesman for the U.S. Secret Service, verified that the agency has done business with Datong in the past. But he would not comment on whether the agency still does business with Datong or what sort of technology it has bought from the company in the past.

Representatives from Datong did not return requests for comment. And the Metropolitan Police force is not commenting on the news.

While government agencies use technologies, such as the ones developed by Datong, to keep tabs on suspected criminals and terrorists, civil liberties and privacy watchdogs fear that increasing use of these types of technology can also lead to abuses and privacy violations.

"The problem with this kind of technology is that it means that the police and law enforcement do not have to go through a cell phone provider to gain access to information that can be obtained via someone's cell phone," said Jennifer Lynch, a staff attorney for the Electronic Frontier Foundation, a San Francisco-based nonprofit that works to protect privacy rights in the Internet age. "The law enforcement agency controls access to the interception of the communication data."

Lynch said that even though U.S. cell phone providers haven't had a terrific track record of challenging law enforcement requests for data, at least there is some other organization involved in the process that could potentially put the brakes on.

Lynch, whose group has been compiling information about cell phone tracking technologies used by law enforcement, said that the EFF is not familiar with the Datong technology. And she wasn't aware of U.S. agencies that use it. But she said that in 2008, it became known that the FBI had been using similar technology for years called Triggerfish to track cell phone users.

Like Datong's technology, Triggerfish pretends to be a cell tower base station so that mobile handsets connect to it and identify themselves, giving up location and other identifying information. But unlike Datong's technology, Triggerfish does not intercept phone calls, e-mails, text messages, or other data that is being transmitted. It appears from The Guardian article that the Datong technology may be able to intercept messages and phone calls.

"If the Datong devices are collecting communications data, that is a much higher level of invasion of privacy," she said.

Still, even the location information that the FBI and other agencies may gather about suspects or other people of interest in various investigations can be an invasion of privacy. And groups, such as the EFF and the American Civil Liberties Union are pushing to require stricter standards for law enforcement to use this kind of technology. Specifically, the EFF is part of a group that is asking Congress to update the Electronic Communications Privacy Act of 1986 to require that these types of technologies require a warrant in order to get permission to use them.

Lynch said that the EFF's own investigation has found that instead of getting warrants for the use of the Triggerfish technology, the FBI has obtained court orders to use the technology. While obtaining court orders is still a legal process that could help prevent the technology from being misused or abused, Lynch said that it would be better if the FBI is required to get a warrant since a court order requires a much lower legal standard.

For people who are worried that they may get caught up in a government surveillance network, such as the one described by The Guardian, security analyst and blogger Richi Jennings has posted a few recommendations on his blog Input/Output for avoiding surveillance. Unfortunately, it doesn't look like there is much an individual can do--other than turn off his or her phon--to avoid being tracked.