Follow me here. It looks like information being collected by the NSA within the PRISM program is filtered to exclude known Americans, but the real effort to exclude the data comes after they have started to collected it.
Here are the slides over at the Washington Post. Go over, take a look and read the attached notes. Here is the note on the first slide, with my emphasis in bold.
This slide describes what happens when an NSA analyst “tasks” the PRISM system for information about a new surveillance target. The request to add a new target is passed automatically to a supervisor who reviews the “selectors,” or search terms. The supervisor must endorse the analyst’s “reasonable belief,” defined as 51 percent confidence, that the specified target is a foreign national who is overseas at the time of collection.
So they are looking for 51 percent confidence the communication is a foreign national overseas. That means there is a 49 percent chance they are targeting communications by Americans on American soil right? This is the first “filter.”
There is additional filtering mentioned on the first slide. The FBI consults a database to ensure the “selectors” do not match known Americans. On the second slide, they mention systems called FALLOUT and CONVEYANCE which seem to be additional filtering used to “reduce the intake” of information about Americans.
Going back to slide 1, there are multiple (3) references to the phrase “Pending Stored Comms” and one reference to “Stored Comms Released.” Also on the left side of the slide there are two reference points mentioning “Surveillance.”
I could be wrong, but it looks to me like they start “storing” communications (that means they are collecting them) immediately after the NSA analyst proves 51 percent confidence – agreed on by a supervisor – the target is not a US citizen within the USA. They keep surveillance going and store communications somewhere while the FBI does their review and FALLOUT and CONVEYANCE does their final sweep.
At some point, the communications identified as from citizens in-country by the FBI, FALLOUT and CONVEYANCE filters would be deleted, right? Or does it just remain in “storage?” In short, they are collecting the information based on one or two people’s opinion, and supposedly not looking at it until it goes through the filters to ensure they are not American targets.
On April 5, according to [the fourth side released by the Post], there were 117,675 active surveillance targets in PRISM’s counterterrorism database. The slide does not show how many other Internet users, and among them how many Americans, have their communications collected “incidentally” during surveillance of those targets.