The NSA keeps using this "54 terror plots thwarted" rhetoric, but there has never been any information released to back up that claim.
From Sen. Patrick Leahy, after reading the full classified list:
“We've heard over and over again the assertion that 54 terrorist plots were thwarted” by the two programs, Leahy told Alexander at the Judiciary Committee hearing this month. “That's plainly wrong, but we still get it in letters to members of Congress, we get it in statements. These weren't all plots and they weren't all thwarted. The American people are getting left with the inaccurate impression of the effectiveness of NSA programs.”
(http://www.propublica.org/article/claim-on-attacks-thwarted-...)
From Sen. Patrick Leahy, after reading the full classified list:
“We've heard over and over again the assertion that 54 terrorist plots were thwarted” by the two programs, Leahy told Alexander at the Judiciary Committee hearing this month. “That's plainly wrong, but we still get it in letters to members of Congress, we get it in statements. These weren't all plots and they weren't all thwarted. The American people are getting left with the inaccurate impression of the effectiveness of NSA programs.” (http://www.propublica.org/article/claim-on-attacks-thwarted-...)