Deepfakes are fake videos created or altered with AI software that show a person saying and doing things they never said or did.
Well-made deepfakes are incredible technically; the line between a good deepfake and real life is essentially indistinguishable.
The latest example is from YouTuber Ctrl Shift Face, who edited a video of actor Bill Hader appearing on Late Night with David Letterman back in 2008.
During Hader's appearance on the show, he tells the story of meeting Tom Cruise for the first time at a table read.
As Hader impersonates Cruise in the deepfake, posted to YouTube last week, his face in the deepfake subtly morphs into Cruise's.
Later in the clip Hader impersonates actor Seth Rogen, and the same happens.