Remotely Eavesdropping on Cell Phone Microphones

I give a talk called “The Future of Privacy,” where I talk about current and future technological developments that erode our privacy. One of the things I talk about is auditory eavesdropping, and I hypothesize that a cell phone microphone could be turned on surreptitiously and remotely.

I never had any actual evidence one way or the other, but the technique has surfaced in an organized crime prosecution:

The surveillance technique came to light in an opinion published this week by U.S. District Judge Lewis Kaplan. He ruled that the “roving bug” was legal because federal wiretapping law is broad enough to permit eavesdropping even of conversations that take place near a suspect’s cell phone.

Kaplan’s opinion said that the eavesdropping technique “functioned whether the phone was powered on or off.” Some handsets can’t be fully powered down without removing the battery; for instance, some Nokia models will wake up when turned off if an alarm is set.

Seems that the technique is to download eavesdropping software into the phone:

The U.S. Commerce Department’s security office warns that “a cellular telephone can be turned into a microphone and transmitter for the purpose of listening to conversations in the vicinity of the phone.” An article in the Financial Times last year said mobile providers can “remotely install a piece of software on to any handset, without the owner’s knowledge, which will activate the microphone even when its owner is not making a call.”

Nextel and Samsung handsets and the Motorola Razr are especially vulnerable to software downloads that activate their microphones, said James Atkinson, a counter-surveillance consultant who has worked closely with government agencies. “They can be remotely accessed and made to transmit room audio all the time,” he said. “You can do that without having physical access to the phone.”

[…]

Details of how the Nextel bugs worked are sketchy. Court documents, including an affidavit (p1) and (p2) prepared by Assistant U.S. Attorney Jonathan Kolodner in September 2003, refer to them as a “listening device placed in the cellular telephone.” That phrase could refer to software or hardware.

One private investigator interviewed by CNET News.com, Skipp Porteous of Sherlock Investigations in New York, said he believed the FBI planted a physical bug somewhere in the Nextel handset and did not remotely activate the microphone.

“They had to have physical possession of the phone to do it,” Porteous said. “There are several ways that they could have gotten physical possession. Then they monitored the bug from fairly near by.”

But other experts thought microphone activation is the more likely scenario, mostly because the battery in a tiny bug would not have lasted a year and because court documents say the bug works anywhere “within the United States”–in other words, outside the range of a nearby FBI agent armed with a radio receiver.

In addition, a paranoid Mafioso likely would be suspicious of any ploy to get him to hand over a cell phone so a bug could be planted. And Kolodner’s affidavit seeking a court order lists Ardito’s phone number, his 15-digit International Mobile Subscriber Identifier, and lists Nextel Communications as the service provider, all of which would be unnecessary if a physical bug were being planted.

A BBC article from 2004 reported that intelligence agencies routinely employ the remote-activation method. “A mobile sitting on the desk of a politician or businessman can act as a powerful, undetectable bug,” the article said, “enabling them to be activated at a later date to pick up sounds even when the receiver is down.”

For its part, Nextel said through spokesman Travis Sowders: “We’re not aware of this investigation, and we weren’t asked to participate.”

EDITED TO ADD (12/12): Another article.

Posted on December 5, 2006 at 6:29 AM

Sidebar photo of Bruce Schneier by Joe MacInnis.