HMM: Market Data Firm Spots the Tracks of Bizarre Robot Traders. “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.”

UPDATE: Some thoughts here on what’s going on from Brian Erst.