Google has released a database of 3,000 deepfakes - videos that use artificial intelligence to alter faces or to make people say things they never did. The videos are of actors and use a variety of publicly available tools to alter their faces. The search giant hopes it will help researchers build the tools needed to take down "harmful" fake videos. There are fears such videos could be used to promote false conspiracy theories and propaganda. Deepfake technology takes video and audio clips of real people, often politicians or celebrities, and uses artificial-intelligence techniques to alter them in some way, for instance putting words in their mouth or transposing their head on to body of an actor in pornography. Since their first appearance in 2017, many open-source methods of generating deepfake clips have emerged.