The paper quotes national security officers and private sector sources with knowledge of the program and the technology used.
The sources say the program has failed in nearly cases to even come up with "probable cause" for spying on the people who've been targeted. Something lawyers say could raise serious questions about the legality of the program.
"National security lawyers, in and out of government, said the washout rate raised fresh doubts about the program's lawfulness under the Fourth Amendment,because a search cannot be judged 'reasonable' if it is based on evidence that experience shows to be unreliable."
The report says fewer than 10 US citizens a year have raise sufficient suspicion to warrant follow up wiretaps.