My favorite quote from this article, discussing the spontaneous market crash last April:
The trading bots visualized in the stock charts in this story aren’t doing anything that could be construed to help the market. Unknown entities for unknown reasons are sending thousands of orders a second through the electronic stock exchanges with no intent to actually trade. Often, the buy or sell prices that they are offering are so far from the market price that there’s no way they’d ever be part of a trade. The bots sketch out odd patterns with their orders, leaving patterns in the data that are largely invisible to market participants.
These bots are making 56,000 offers a second. It sure looks to me like something not-human is actually happening here, though it could be the result of gross incompetence, I suppose. Or maybe that was a test run.
But it looks to me kinda like an attempt at saying “hello.”