Former Treasury Secretary Larry Summers was on “Sunday Morning Futures,” where he discussed the markets in Japan and Michael Lewis’ new book, “Flash Boys.”

Summers said that the place in the world where risks are currently most underestimated is Japan.

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“Given the magnitude of its debt problems, Japan is walking on a very narrow ledge,” he told Maria Bartiromo.

Summers also weighed in on “Flash Boys,” a new book by Michael Lewis that claims the stock market is rigged.

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"I think that it’s a staggering exaggeration to say that the market is rigged. That said, high frequency trading has been a concern of mine for a long time,” he said.

Summers said high frequency trading is a proper area for concern and hopes it will receive more attention going forward.