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updated 4/17/2013 6:50:40 PM ET 2013-04-17T22:50:40

Hours following the blasts at the Boston Marathon finish line Monday (April 15), cellular networks buckled under the pressure of tens of thousands of people using their phones to call loved ones. Soon to follow were news reports that cellphone service was shut down intentionally to prevent possible remote detonations of further bombs using cellphones.

These reports were quickly debunked by wireless carriers AT&T, Sprint, T-Mobile and Verizon, which countered that cellphone networks were strained from congestion but were never shut down. Boston law enforcement officials did not return our multiple calls asking whether cellular networks were intentionally disrupted on Monday.

Verizon issued the statement: "Verizon Wireless has not been asked by any government agency to turn down its wireless service." However, both Verizon and AT&T representatives said they had no comment when we asked if they ever have in the past or ever would in the future shut down cellular service based on a law-enforcement request.

Wireless  experts say it's unlikely authorities in Boston disrupted overall cellular service, but say that jamming signals to create cellular "dead zones" is an increasingly common tactic among federal agencies as well as state and local law enforcement in unique circumstances. John Minor, a wireless industry analyst, said law enforcement doesn't need to coordinate with wireless carriers to black out pockets of cellphone service.

Instead, Minor said, authorities can use powerful jammers that fill the same radio frequency that cellphones use with radio "noise," knocking nearby handsets and wireless devices offline within a 50- to 500-yard range. [See also: Cell Phone Jammer Puts Brakes on Driver Chats ]

Jamming wireless signals is a closely held law enforcement tactic used for crowd control, warrant execution and standoffs (to prevent communication between a suspect and outside parties) and in prisons and jails (to prevent the use of contraband cellphones by inmates). Even the presidential motorcade is known to use jamming technology to foil possible detonation of remote-controlled bombs along its route. 

The use of jamming is controversial. It's a blunt instrument, said Harlin McEwen, with The International Association of Chiefs of Police. "The public is increasingly depending on commercial services to report emergencies and suspicious activities," McEwen said. "Every time you make the choice to disrupt service, it has to be with a lot of thought and done judiciously."

Jamming wireless signals in Boston, McEwen said, could have prevented the public from calling in tips of suspicious activities to law enforcement following the blasts.

Jamming free speech

The U.S. military has used jamming to stop the threat of roadside cellphone-activated bombs in Iraq and Afghanistan. But repressive regimes have also used the method. In 2011, the Egyptian government reportedly used cellphone jammers (in addition to shutting down the Internet) to cripple protesters from coordinating demonstrations.  Cellphone blackouts used to control crowds have also caused controversy closer to home. 

In April 2011 in San Francisco, the subway phone service was shut down (not jammed) by the Bay Area Rapid Transit Authority (BART). Officials feared that protesters were organizing a mob to demonstrate against the death of a man during a confrontation with transit police. The move sparked outrage among First Amendment advocates and fed into future protests, including  Occupy Wall Street.

Under the Federal Communication Act of 1934, it's illegal for private citizens to own or operate jamming equipment. But the FBI and the Secret Service have waivers allowing them to use the devices, according to Minor, who calls the practice an "open secret." [See also:  Law Enforcement Tracks Phones With Phony Cell Towers ]

Furthermore, last year the National Security Telecommunications Advisory Committee gave state-level Department of Homeland Security advisers the authority to terminate wireless service in "a localized area or within an entire metropolitan area," according to a report (PDF) issued by the agency.

Advocacy groups such as the Center for Democracy and Technology and the Electronic Frontier Foundation argue that wireless blackouts violate the public’s First Amendment rights. Both argue the FCC should have stricter oversight of when wireless networks are shut down.

Email Tom Spring  or follow him@zpring. Follow us@TechNewsDaily, on Facebook  or on Google+

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