How many terrorist plots since 9/11 ?

September 11, 2001 attacks in New York City: View of the World Trade Center and the Statue of Liberty. (Image: US National Park Service ) (Photo credit: Wikipedia)

One source cites 60:

Abstract

The Heritage Foundation has tracked post-9/11 terrorist plots against the United States in an effort to study the evolving nature of the threat and to garner lessons learned. The best way to protect the United States from terrorism is to ensure a strong and capable domestic counterterrorism enterprise—and to understand the continuing nature of the terror threat. The Boston Marathon bombing was the 59th publicly known terror plot against the United States since 9/11. In a political environment of sequestration on the one hand, and privacy concerns on the other, there are those on both sides of the aisle who want to cut counterterrorism spending and restrict the scope of U.S. intelligence agencies. But the long war on terrorism is far from over. Most disturbingly, an increasing number of Islamist-inspired terrorist attacks are originating within America’s borders. The rise of homegrown extremism is the next front in the fight against terrorism, and Congress and the Administration must take it seriously. This Special Report features up-to-date information on all 60 plots, and the authors describe a plan for a comprehensive homeland security strategy.

http://www.heritage.org/research/reports/2013/07/60-terrorist-plots-since-911-continued-lessons-in-domestic-counterterrorism

Dr. Erik Dahl of the Naval Post Graduate School dissects 109 sneak attacks on America in his new book, "Intelligence and Surprise Attack: Failure and Success from Pearl Harbor to 9/11 and Beyond."
http://www.amazon.com/Erik-J.-Dahl/e/B00DW1NFD8
In a recent talk, Dahl stated his thesis:  success usually flowed from good human intell.

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