I remember when some Syrian kids almost crashed the whole thing.
They hacked a media outlet twitter feed and posted a bogus tweet about a terrorist attack on the White House.
Now I am not saying these hackers knew what would happen next but maybe they did making it some 'Dr. Otto and the Riddle of the Gloom Beam' level of evil genius.
These trading robots suddenly started throwing a shit fit. They are plugged in 24/7 scouring trends on the internet. When they saw there was 'an attack on the White House' being machines they had no way of knowing or quickly deducing there were shenanigans afoot. For these machines this was 100% real so it was time to sell. And sell they did. Because they are programmed to buy and sell without human intervention. By the time their panicked operators pulled the plug the machines had initiated what would have been an unprecedented apocalyptic sell-off. You can look up the drop on the graph yourself. It's enormous. And all due to just one instance of shitposting. That terrifies me.