Update (Sept. 29 at 1:42 am UTC): This article has been updated with new comments from Zano head of marketing and growth Quinten van Welzen.

Zano has rolled back approximately one month of blockchain history after a vulnerability involving Gateway Addresses allowed unauthorized ZANO and Freedom Dollar tokens to enter circulation, according to the project’s core team.

The Zano blockchain was restarted at block 3,833,000, immediately before Hard Fork 6, which introduced the affected feature. The recovery requires participating nodes, miners, stakers, exchanges and other services to adopt the update, the team said Sunday.

“The total number of unauthorized assets was considerable,” van Welzen told Cointelegraph.

The rollback invalidates a month of legitimate transactions along with the unauthorized tokens. As a result, transactions made during that period will no longer appear on the recovered chain. The rollback also cannot reverse payments that have already been settled on other blockchains, meaning assets moved off Zano during the affected window are beyond the recovery’s reach.

Full rollbacks of a live blockchain are rare, since they depend on broad coordination across everyone running the network. The most prominent precedent came in 2016, when the Ethereum community voted to reverse the effects of the DAO exploit through a hard fork, splitting the network, with opponents of the intervention continuing the original chain as Ethereum Classic.

Zano said it is working to account for losses and will publish a reimbursement and claims process, the details of which had not been released at the time of publication.

“Doing nothing meant unauthorized ZANO and fUSD in circulation without limit, diluting every holder and breaking the most basic promise a currency makes: a fixed supply,” van Welzen said in an X post. “It would also tell every future attacker that exploited coins get to keep their value. No project survives that.”

Zano identifies Gateway Address exploit

Zano had not released a post-mortem at the time of publication, but confirmed that the issue originated in Gateway Addresses. The feature was developed to make it easier for bridges, exchanges and payment services to integrate with Zano by allowing them to manage funds through a single, account-style balance similar to those used on other blockchains.

Before Gateway Addresses, Zano’s standard wallets tracked funds as separate transaction outputs, known as UTXOs — the model used by Bitcoin — rather than as a single account balance. Exchanges and other services had to scan the blockchain to identify incoming payments, track those outputs and select which outputs to spend when processing withdrawals.

In comments to Cointelegraph, van Welzen confirmed that active addresses are not active on the updated chain. They will return after the Gateway Address code has undergone review, auditing and testing.

Zano launched in May 2019 as a layer-1 blockchain focused on private payments. Its standard private transactions conceal senders, receivers, transferred amounts and asset types. In addition to its native ZANO token, the blockchain allows users to deploy and mint custom digital assets. Freedom Dollar, or fUSD, is one such token operating on the Zano blockchain.

“Restarting the chain from before Hard Fork 6 costs a month of history, and it costs trust, which we’ll have to earn back,” van Welzen said.

“But it restores the supply everyone signed up for, and it leaves a path to rebuild. Which is better than 7 years of hard work left to die. We know it hurts. But not doing it would have hurt more.”