Barton Gellman, he had given a keynote presentation at the Purdue University about the NSA, Edward Snowden, and national security journalism in the age of surveillance. The University stated that they would release footage of the keynote presentation with a permalink, so the keynote presentation could be enjoyed by many others.
Gellman explains that after unexplained delays, he fineally got an letter which explained that the keynote presentation could not be released as it contained classified and leaked information which had been tagged ‘critical’ by the Defense Department. The Purdue University agreed (at that time), and they deleted the footage from their servers and networks.
Barton Gellman has gone full public on a post which you can find at Arstechnica. I strongly urge you to read it.