In early 2013, before Glenn Greenwald was convinced that Edward Snowden, who assumed the pseudonym "Cincinnatus," was who he said he was, Snowden evidently created a video tutorial in order to coach Greenwald through the process of installing encryption software on his computer so NSA files and other messages could be securely shuttled between the two.
Greenwald initially ignored Cincinnatus' messages and the tutorial. You might recall how Greenwald, ostensibly the most prominent reporter covering the biggest tech story of the year, referred to himself as "basically technically illiterate."
Note at timecode 3:20, Snowden warns Greenwald about encryption and airport security in England, which Greenwald failed to consider before sending his spouse through Heathrow with encrypted materials.
The Intercept's Dan Froomkin tweeted the link to the video earlier today, though The Washington Post reports that it was posted on Vimeo by someone called "anon108" last year. Neither Greenwald nor Froomkin have confirmed that the video was created by Snowden, but clearly the altered voice on the video is Snowden's, based on his now well-known manner of speaking and accent.