"Intelligence requires secrets. And secrecy is under assault. The future of US intelligence effectiveness depends to a very significant degree on keeping its secrets about collection sources and methods and analytical techniques. When secrecy is breached, foreign targets of US intelligence--such as adversary countries and terrorists--learn about, and then often develop countermeasures to, US intelligence techniques and operations. As a result, the effectiveness of intelligence declines, to the detriment of the national security policymakers and warfighters, and the citizenry that it is meant to serve. This paper covers how significant the issue of media leaks can be."
Center for the Study of Intelligence: https://www.cia.gov/library/center-for-the-study-of-intelligence/index.html
Studies in Intelligence, v.47 no.1, 2003