On March 12, 2020, one bot acquired $8.32 million worth of ETH and paid absolutely nothing for it. There was no hack and no exploit. Just a broken assumption inside one of DeFi’s most trusted protocols and a 40-minute window that nobody saw coming.
Here’s the story.
What MakerDAO’s System Was Built to Do
MakerDAO lets users lock ETH as collateral to borrow DAI. When that collateral loses too much value, the vault gets liquidated through an on-chain auction. Bots called keepers bid DAI to purchase the collateral, the debt gets covered, and the protocol stays solvent.
The entire mechanism relied on one assumption holding true: that competing bots would always show up.
The 40 Minutes That Broke DeFi
ETH dropped 43% in hours that day. Hundreds of vaults went underwater at the same time, and every keeper bot on the network tried to respond at once. Ethereum could not handle the traffic. Gas prices spiked 10x and most keeper bots ran on fixed gas settings, leaving their transactions stuck in the mempool and going nowhere.
Auctions were opening and nobody was bidding.
One bot noticed. It submitted a bid of 0 DAI, waited out the timer, and collected real ETH for free when no competing bids arrived. Then it did it again. For nearly 40 minutes, that one bot swept auction after auction at zero cost, walking away with $8.32 million in ETH before the network stabilized and other bots could get back in.
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MKR Holders Paid the Price
MakerDAO was left with $4.5 million in bad debt, something the protocol had never faced before. MKR holders voted to mint new tokens and sell them into the open market just to cover the shortfall, diluting every existing holder in the process.
The contract had done exactly what it was coded to do. The auction ran correctly. The bot followed the rules.
As one observer summed it up in the thread that is now going viral on X: “The protocol didn’t break because the rules were wrong. It broke because the design assumed continuous market participation at the exact moment the market became least functional.”
Why the Story Still Matters
Analysts say every major DeFi liquidation system built after 2020 traces its risk design back to one 40-minute window. Black Thursday changed how the entire industry approaches risk when liquidity, bots, and block space fail all at once.
With DeFi liquidations back in the headlines and billions under pressure with the ongoing US-Israel-Iran war, the lesson is hitting differently right now.
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