Hackers reportedly stole over $600 million from a blockchain network this past week in one of the biggest hack attacks in the cryptosphere to date. Thieves targeted Ronin Network, the blockchain behind Axie Infinity, a popular online game with roughly 2.5 million monthly users.

Ronin Network said on March 23, 2022, hackers took 173,600 Ether (the second largest cryptocurrency by volume behind Bitcoin), along with $25.5 million in dollar-linked coin known as USDC. The amount was drained in just two transactions, according to the company, which claims the funds are still in the hacker’s cryptocurrency wallet. Ronin Network did not discover the hack until March 29.

“We are working with law enforcement officials, forensic cryptographers, and our investors to make sure all funds are recovered or reimbursed,” Ronin said in a statement.

The heist exposes the vulnerability of blockchain bridges, a tool that allows people to transfer cryptocurrency from one blockchain to the next. Bridges move hundreds of millions of dollars in cryptocurrency despite security holes.

Ronin said the attacker used hacked private keys to forge the withdrawals. No one noticed the missing coin for six days, until a legitimate user reported being unable to withdraw 5,000 Ether from the bridge.

As cryptocurrency becomes more prevalent in society, so does theft. Chainalysis reported that in 2021, $3.2 billion of cryptocurrency was stolen, six times the amount from 2020.

Unfortunately, the hack of @Ronin_Network is the latest in a series of DeFi thefts. In 2021, $3.2B in crypto was stolen from individuals and services — 6x the amount stolen in 2020. https://t.co/MMzB2cYihS pic.twitter.com/UBweiiovvB

— Chainalysis (@chainalysis) March 29, 2022