"National Security Agency." The Columbia Encyclopedia, Sixth Edition. 2008. Encyclopedia.com. 8 Nov. 2009 <http://www.encyclopedia.com>.
"National Security Agency." The Columbia Encyclopedia, Sixth Edition. 2008. Encyclopedia.com. (November 8, 2009). http://www.encyclopedia.com/doc/1E1-NatlSecAg.html
"National Security Agency." The Columbia Encyclopedia, Sixth Edition. 2008. Retrieved November 08, 2009 from Encyclopedia.com: http://www.encyclopedia.com/doc/1E1-NatlSecAg.html