ultimate solution that would prevent a repeat “Knightmare”

"Singer and others warned that the August 2012 Knight trading disruption will happen again at another firm.

“It absolutely can. Most trading today is driven by machine,” according to Larry Tabb, founder of the Tabb Group, an industry consultancy. “And to the extent that programming is done by people, and given the complexity of the market structure, there will be problems that people don’t expect.”
The problem, Tabb added, is the actual trading, or what is called execution, is earning firms very little, so they don’t have the best systems.

One option might be a mandated kill switch, which would automatically limit how much damage could be done by trading systems.

...the ultimate solution that would prevent a repeat “Knightmare” — and others before and since — will not come from regulators, says Singer. He says it must come from the industry, with all firms chipping in to construct a backup trading system."

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