U.S. cryptocurrency firm Harmony has confirmed a major cyberattack in which hackers stole around $100 million worth of digital coins from one of the company’s key products.

Harmony explained that the cyber theft hit its Horizon “bridge,” a tool used to transfer crypto between different blockchains.

According to Elliptic, a firm that tracks publicly available blockchain data, the hackers stole various Harmony cryptocurrencies, including Ether, Tether and USD Coin. The hackers then exchanged the stolen digital coins for Ether via decentralized cryptocurrency exchanges.

While the company gave no further details about the attack, Harmony said in a tweet that it was “working with national authorities and forensic specialists to identify the culprit and retrieve the stolen funds.”

“We are currently narrowing down the potential attack vectors while working to identify the culprit,” a spokesperson said. Harmony had already tried to contact the hacker via a transaction to their crypto wallet address.

The sources for this piece include an article in Reuters.