Offchain Labs co-founder Ed Felten said there were one or two fraud challenges submitted on a version of Arbitrum running on the Ethereum proof-of-work fork after the Merge, which was defeated.

Not a single fraud proof has been submitted on Arbitrum since it first launched its mainnet with the built-in security feature in August 2021, according to Ed Felten, co-founder and chief scientist of the Arbitrum-building Offchain Labs.

Operating as an Ethereum layer-2, Arbitrum’s interactive, multi-round fraud proofs work by allowing a layer-1 verifier contract to decide whether the challenger’s fraud-proof submission is valid. If so, the fraudulent validator’s stake is slashed.

Fraud proofs are submitted by challenging validators when it considers another validator to have fraudulently or otherwise incorrectly assembled an incoming batch of transactions into the next block.

However, Arbitrum’s mainnet is yet to see a fraud-proof attempt let alone a successful challenge, Felten told Cointelegraph at Korean Blockchain Week on Sept. 4:

“Not on mainnet. We did have one or two on Ethereum proof-of-work (POW). After the Merge, [...] there was a version of Arbitrum running on the Ethereum POW fork and somebody did try to steal all the data and there was a successful challenge which defeated that.”
Felten said few fraud proof attempts have been made because malicious-intended validators are risk losing their entire stake.

Source - Coin Telegraph