A technician inspects the backside of a cryptocurrency mining farm ein Saint Hyacinthe, Quebec. Wormhole, a popular bridge to move cryptocurrency from one blockchain to another, saw approximately $325 million stolen by hacker. (LARS HAGBERG/AFP via Getty Images)

Wormhole, a popular bridge to move cryptocurrency from one blockchain to another, saw 120,000 Ether — approximately $325 million — stolen by hackers in a move that could destabilize the bridge.

"The wormhole network was exploited for 120k wETH [Wormhole Ether]. ETH will be added over the next hours to ensure wETH is backed 1:1. More details to come shortly," tweeted Wormhole at 5:30 pm ET. "ETH will be added over the next hours to ensure wETH is backed 1:1"

Wormhole shut down service to investigate. Two hours later, Wormhole followed up with a tweet saying the vulnerability had been patched. What the vulnerability had been remains unclear.

The popular bridge allows interoperability between the Ether and Solana blockchains through smart contracts. But the value is contingent on holding the assets on both chains to back each other in a one-to-one ratio.

If the assets disappear, “there are no assets backing the cross-chain token, and then the token no longer has any value. The cross-chain token is of the asset on the other chain. So essentially, it makes the wrap tokens worthless," said Max Galka, CEO of the blockchain forensics firm Elementus.

Galka said that replacing $325 million in Ether would be complicated without negotiating the return of the stolen funds; it would be a lot of coins to try to purchase in a short period. It would amount to 3.5% of the daily volume of Ether transactions.

But, he added, laundering $325 million in cryptocurrency in a way that would allow the criminals to cash out without being caught would be extremely difficult.

"I would not immediately assume that the funds are completely gone," he said. "That these days it is not trivial to be able to cash out crypto in this size. There have been a lot of cases recently where the funds have been returned."

Galka noted that the first transactions on the criminal wallets took place Tuesday morning and were from the anonymization service Tornado cash, meaning the thieves had at minimum experimented with one such service. Mixers are not, however, designed to handle hundreds of millions of dollars in funds at a time.

In several recent cases, large cryptocurrency and DeFi services have been able to negotiate the return of funds with an attacker for a reduced rate after exchanges, coins and other services agree not to accept the stolen loot.

The long-term prospects of bridges have been questioned before. Vitalik Buterin, creator of Ethereum, argued last month that it was always safer to hold coins on a specific cryptocurrency blockchain rather than a bridge due to the potential of instability of either of the two currencies.

"I don't think that these bridges are really the future of crypto and are viable long term for really just this reason,” said Galka. “Holding ether on the Ethereum blockchain is quite secure. Holding Solana on the Solana blockchain is quite secure. But once you get into these, these cross chain assets, you run all sorts of different risks."