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."
Because modern handsets are miniature computers, downloaded software could modify the usual interface that always displays when a call is in progress. The spyware could then place a call to the FBI and activate the microphone--all without the owner knowing it happened. (The FBI declined to comment on Friday.)
"If a phone has in fact been modified to act as a bug, the only way to counteract that is to either have a bugsweeper follow you around 24-7, which is not practical, or to peel the battery off the phone," Atkinson said. Security-conscious corporate executives routinely remove the batteries from their cell phones, he added.