Even before Snowden, everyone (terrorists included) knew that the NSA was devoting vast resources to spying on terrorists, building a huge data center in Utah to store communication intercepts, etc., etc. Quite a while before anyone had heard of Snowden, Osama bin Laden was very paranoid about his communication security because he knew that the U.S. was capable of eavesdropping on cellphone conversations. Snowden's only surprising revelations were that the NSA was spying on all U.S. citizens and on friendly governments like Germany.
It's getting harder to thwart terrorists using outdated techniques they know are compromised. Shocked.
Because until Snowden they had so much success arresting random muslims^W^Wterrorists.