(Bloomberg) -- A crypto service used to move tokens between blockchains suffered an unexplained outflow of assets worth more than $120 million, according to digital-asset security specialist BlockSec.

The Multichain protocol tweeted on Friday that “lockup assets” have been “moved to an unknown address abnormally,” and added that “the team is not sure what happened and is currently investigating.”

BlockSec later wrote on Twitter that the tokens have now been distributed across six crypto wallets but refrained to hypothesizing about the cause.

Multichain is one of a number of services that try to make disparate digital ledgers interoperable. Such so-called crypto bridges have proved to be vulnerable to hackers, who stole about $2 billion from them last year alone, based on estimates from Chainalysis.

The Multichain protocol — a decentralized application that deploys self-executing, software-based smart contracts — advised against accessing its services and told users to revoke contract approvals related to the bridge.

CEO AWOL

In late May, Multichain said it had “experienced multiple issues” and was unable to contact its chief executive officer — whom it identified as Zhaojun — to “obtain the necessary server access for maintenance.”

The total value of assets locked on Multichain tops $1.2 billion, making it the third largest crypto-sector bridge, according to data from DefiLlama.

Changpeng ‘CZ’ Zhao, founder of the largest crypto exchange Binance, tweeted that it “looks like another hack” has hit Multichain.

Multichain’s native token MULTI slid 17% to $2.59 as of 7:53 a.m. in London on Friday, according to figures from CoinGecko.

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