(Bloomberg) -- Two hacking groups linked to North Korea were responsible for the theft of $100 million in an attack on a crypto service last year, the Federal Bureau of Investigation said on Monday.

The Lazarus and APT38 outfits perpetrated the June attack on US-based blockchain specialist Harmony’s Horizon Bridge, the FBI said in a statement.

Horizon is an example of software that allows crypto tokens to move between different blockchains. Such cross-chain bridges became a soft target for hackers last year, with about $2 billion worth of crypto assets stolen in 13 separate bridge hacks, according to Chainalysis.

On January 13, the North Korea-linked hackers used a privacy protocol called Railgun to launder $60 million worth of Ether, the FBI said. Some of this was sent to several crypto exchanges and converted to Bitcoin, the bureau said.

Changpeng Zhao, founder of the world’s largest crypto exchange Binance Holdings Ltd., said on Twitter last week that his firm helped the Huobi platform to freeze some the funds and recover 124 Bitcoins.

Lazarus was also blamed for the $600 million Ronin bridge hack. 

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