Hackers have stolen $100 million in cryptocurrency from Horizon, a blockchain bridge, in the latest massive decentralized finance heist.

There aren’t enough details about the hack, but Harmony, the developers behind Horizon, said they identified the theft Wednesday morning. Harmony said that they believe one account is the culprit.

“We have begun working with national authorities and forensic specialists to identify the culprit and retrieve the stolen funds,” the start-up said in a tweet late Wednesday.

In a follow-up tweet, Harmony said it’s collaborating with the Federal Bureau of Investigation and multiple cybersecurity firms to investigate the attack.

Blockchain bridges are  big player in the DeFi space. The technology offers a medium for users to send their assets from one blockchain to another. In Horizon’s case, users can transfer tokens from the Ethereum network to Binance Smart Chain. Harmony said the attack did not affect a separate bridge for bitcoin.

Bridges “maintain large stores of liquidity,” making them a “tempting target for hackers,” according to Jess Symington, research lead at blockchain analysis firm Elliptic.

“In order for individuals to use bridges to move their funds, assets are locked on one blockchain and unlocked, or minted, on another,” Symington said. “As a result, these services hold large volumes of cryptoassets.”

Harmony has not revealed how the heist occured. But, one investor had raised concerns about the security of its Horizon bridge as far back as April.

The security of the Horizon bridge hinged on a “multisig” wallet that required only two signatures to initiate transactions. Some researchers speculate the breach was the result of a “private key compromise,” where hackers obtained the password, or passwords, required to gain access to a crypto wallet.

The heist adds up to the plethora of negative news in the crypto market. Crypto lenders Celsius and Babel Finance halted withdrawals after a dramatic decline in the value of their assets which resulted in a liquidity crunch. On the other hand, beleaguered crypto hedge fund Three Arrows Capital could be set to default on a $660 million loan from brokerage firm Voyager Digital.