With the Obama administration aggressively prosecuting government workers for revealing classified information to the media, journalists are finding it more difficult in the age of improved surveillance technology to protect their sources.
It used to be that the government had to pressure the journalists directly for the identities of their sources, but increasingly they can find out on their own by keeping an eye on government workers with security clearances. -db
From an analysis in The New York Times, February 11, 2012, by Adam Liptak.