The FBI says while intercepting phone and internet conversations in terrorism investigations, they sometimes tap the wrong number. Critics point to the need to revise wire tap provisions detailed in the Patriot Act.

FBI spokespersons would not say how often these mistakes are happening, but pointed out that incriminating evidence mistakenly collected is not admissible in a criminal case. There is no way of knowing whether it is used to begin new investigations.

In a recent report from the Justice Department inspector general, 38,514 hours exist in the FBI’s backlog of intercepted conversation, what the FBI calls a “collection of materials from the wrong sources, due to technical problems.”

Ed Cogswell, FBI spokesman said that the FBI is required to inform the secret court that approved the initial intercept when a collection error occurs. The FBI cannot say whether people are notified they were mistakenly tapped, or that wrongfully intercepted numbers are removed from bureau records.

“What do you mean you are intercepting the wrong subject,” said James Dempsey, executive director of the Center for Democracy and Technology. “How often does this occur? How long does it go on for?”

While the FBI has acknowledged such mistakes in the past, representatives of the Electronic Privacy Information Center claim advances in digital communication are making it more difficult to “conduct wiretapping in a surgical way.”

In 2004, a court that operates secretly under the Foreign Intelligence Surveillance Act issued 1,754 warrants permitting secret searches and surveillance, including wiretaps. These warrants permit surveillance for up to one year without notification.

“They have recorded the information,” said Rep. Bobby Scott, D-Va, “but they’re saying ‘Trust us, we won’t listen to what we recorded.' People ought to be concerned.”