- Ronin Bridge exploit
On March 23 2022, the Ronin Bridge was exploited, with the loss of 173,600 ETH (worth around $590M at current prices and 25.5M worth of USDC). It was said that around 5 out of 9 validators were attacked and controlled during the incident. The main purpose of validators is to create transaction blocks and update data oracles.
Link here for statement by the Sky Mavis team.