Concerned over the spread of fake news on the social networking giant, US President Barack Obama has criticised Facebook, saying fake stories on social networks are spreading lies this election.Speaking at a rally for Hillary Clinton at University of Michigan on Monday, Obama said: "The way campaigns have unfolded, we just start accepting crazy stuff as normal and people if they just repeat attacks enough and outright lies over and over again.""As long as it's on Facebook, and people can see it, as long as its on social media, people start believing it, and it creates this dust cloud of nonsense," he told the gathering.A recent BuzzFeed investigation found that 38 per cent of posts shared from three large right-wing politics pages on Facebook included "false or misleading information, reported www.sfgate.com.A follow-up probe by BuzzFeed revealed how teenagers in Macedonia create fake, pro-Trump news stories that go viral on Facebook.Buzzfeed has also reported tweets encouraging people to vote by text which isn't possible.Facebook has reiterated several times that it is working to improve the filtering of false and misleading stories from the News Feed.