Kurt Eichenwald’s piece for Vanity Fair today has some of the clearest information I’ve yet seen on exactly how the NSA’s data collection programs work, what they’re used for, and the many layers of legal oversight and limitations placed upon them: PRISM Isn’t Data Mining and Other Falsehoods in the N.S.A. “Scandal”.

I can’t stand it.

A few days ago, I wrote in some detail about the National Security Agency’s data-mining program in hopes of calming the hysteria that has been whipped up in the last number of days by incorrect and misleading reports, as well as by plenty of ill-informed commentary based on those errors. At this point, I’ve decided that I need to tell a little bit more.

Some explanation up front: I spent seven years investigating the national-security systems and policies established in the aftermath of the 9/11 attacks for my book 500 Days. I learned a fair amount about the data-mining programs of the N.S.A. and wrote about it. I summarized those findings in my last post. However, now it has become obvious to me that I need to go further than I did in my book, at least in hopes of calming things down. When discussing errors, I’m going to mention “reports” regarding news articles, but I’m not going to identify them—the last thing I want is for this to become a back-and-forth between reporters.

First, the much-ballyhooed PRISM program is not a program and not a secret, and anyone who says it is should not be trusted because they don’t know what they’re talking about.

According to Eichenwald, NSA data-mining of international Internet activity is not only specifically targeted at uncovering terrorist plots, it’s been very effective:

I’m not comfortable getting into too much detail (some sources I interviewed during my reporting for the book placed limits on what I could publicly reveal about active programs as part of their agreement to speak with me). But I can say for a fact that this data-mining and telecommunications program has had significant successes. For example, a network of terrorists at least twice attempted to spirit strontium 90 from Uzbekistan into Kazakhstan; both of those times the smuggling was stopped, once through traditional intelligence activities, and once through the use of the data-mining program. Specific cyber-attacks have been stopped, and strategic plans of terrorist groups obtained. However, it has to be understood that data mining is not a single tool—rather, it is part of a broad array of intelligence-gathering activities, and is rarely used alone to prove a national-security risk.

Read the whole piece — there’s much more interesting info therein.