Math Prodigy Whose Hack Upended DeFi Won’t Give Up His Millions

On Oct. 14, in a house near Leeds, England, Laurence Day was sitting down to a dinner of fish and chips on his couch when his phone buzzed. The text was from a colleague who worked with him on Indexed Finance, a cryptocurrency platform that creates tokens representing baskets of other tokens—like an index fund, but on the blockchain. The colleague had sent over a screenshot showing a recent trade, followed by a question mark. “If you didn’t know what you were looking at, you might say, ‘Nice-looking trade,’ ” Day says. But he knew enough to be alarmed: ...