Hacking is a two way street.

The core developers behind Ethereum, which supports a cryptocurrency similar to bitcoin, launched an assault on an anonymous hacker that stole at least $89 million through its network.

Alex Van Der Sande, lead designer for Ethereum, announced the counterattack on Twitter earlier today. Within four hours, the core developers were able to get back over 7 million of its ether currency, or $89 million, according to the wallet address where the funds are being stored.

The Ethereum developers are trying to retrieve money that had been invested in the Distributed Autonomous Organization (DAO), which raised $150 million in the largest crowdfunding project in history. The anonymous hacker posted an open letter that said he merely exposed a loophole inside ethereum’s smart contract system, and the funds were “claimed legally.” How much the hacker stole is still unclear.

The hack has shaken the faith in Ethereum, which has been attracting interest from corporations including IBM and Microsoft. There are theoretically other ways to retrieve the funds, but they could have also hurt the community’s trust in the network, as Quartz’s Joon Wong Ian wrote: