U.S. crypto firm Harmony said on Friday that thieves stole around $100 million worth of digital coins from one of its key products, the latest in a string of cyber heists on a sector long targeted by hackers.

Harmony develops blockchains for so-called decentralised finance - peer-to-peer sites that offer loans and other services without the traditional gatekeepers such as banks - and non-fungible tokens.

The California-based company said the heist hit its Horizon "bridge", a tool for transferring crypto between different blockchains - the underlying software used by digital tokens such as bitcoin and ether.

Thefts have long plagued companies in the crypto sector, with blockchain bridges increasingly targeted. Over $1 billion has been stolen from bridges so far in 2022, according to London-based blockchain analytics firm Elliptic.

Harmony tweeted that it was "working with national authorities and forensic specialists to identify the culprit and retrieve the stolen funds", without giving further details.

In a statement, Harmony added that it had a global team "working around the clock to address the issue".

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

Elliptic, which tracks publicly visible blockchain data, said the hackers stole a number of different cryptocurrencies from Harmony, including ether, Tether, and USD Coin, which they later swapped for ether using so-called decentralised exchanges.

In March, hackers stole around $615 million worth of cryptocurrency from Ronin Bridge, used to transfer crypto in and out of the game Axie Infinity. The United States linked North Korean hackers to the theft.