http://www.theatlantic.com/politics/archive/2013/06/2-senators-say-the-nsa-is-still-feeding-us-false-information/277187/
a snippet from the article
this same fact sheet states that under Section 702, "Any inadvertently acquired communication of or concerning a US person must be promptly destroyed if it is neither relevant to the authorized purpose nor evidence of a crime." We believe that this statement is somewhat misleading, in that it implies that the NSA has the ability to determine how many American communications it has collected under section 702, or that the law does not allow the NSA to deliberately search for the records of particular Americans. In fact, the intelligence community has told us repeatedly that it is "not reasonably possible to identify the number of people located in the United States whose communications may have been reviewed under the authority" of the FISA Amendments Act.