Two brothers have been arrested by the U.S. Department of Justice for attacking the Ethereum blockchain and stealing $25 million of cryptocurrency during a 12-second exploit, according to an indictment unsealed on Wednesday.

The indictment charges Anton Peraire-Bueno, 24, of Boston, and James Pepaire-Bueno, 28, of New York, with conspiracy to commit wire fraud, wire fraud and conspiracy to commit money laundering.

The charges are significant because they represent a first-of-its-kind criminal action from the U.S. government related to the controversial practice of MEV, or maximal extractable value, whereby the operators of Ethereum (and similar blockchains) preview upcoming transactions from users to earn an extra profit for themselves.

According to Wednesday's indictment, the Pepaire-Bueno brothers exploited MEV-boost, software used by most of the validators that run the Ethereum blockchain.