What is Firo?
Firo is a proof-of-work privacy coin that launched in 2016 as Zcoin and took the Firo name in 2020. Its Lelantus Spark protocol, live since January 2024, lets users hold and send coins with hidden amounts, senders and recipients, while transparent addresses still exist. A network of masternodes adds fast finality and protection against chain rewrites.
Utility Lens
What Firo actually does
Lets people hold and send money privately while still offering view keys and exchange-friendly addresses for situations that need transparency.
- Real-world usage
- earlySpark, Spark Names and masternodes are live and used, but payment activity and trading volume are modest.
- Token necessity
- essentialFIRO pays fees and mining rewards and is the collateral that masternode operators lock up.
- Decentralization
- moderateMining and masternodes are open to anyone, but masternodes now earn 70% of rewards, ChainLocks rely on masternode quorums, and a core team funded by 15% of rewards leads development.
- Track record
- longLive since 2016; a 2019 cryptographic flaw in its old Zerocoin privacy layer let an attacker forge coins, a January 2021 51% attack rolled back over 300 blocks, and a 2026 Spark forging bug needed an emergency fix and hard fork.
What it’s used for
People use FIRO for private payments through Spark addresses and Spark Names, a human-readable alias system, and run masternodes that receive most of the block reward. The project lists smaller centralized exchanges, decentralized exchanges and swap services as places to get it, and a wrapped version trades on Ethereum and BNB Chain.
Role of the FIRO token:
Evidence of real use
- Firo's Lelantus Spark privacy protocol activated on mainnet at block 819300, around January 18, 2024. Source (opens in a new tab)
- On January 18, 2021 Firo suffered a 51% attack that rolled back over 300 blocks and defrauded exchanges, mainly Binance, before ChainLocks were activated. Source (opens in a new tab)
- After a 2024 community vote, Firo pays a fixed 6.25 FIRO per block until 21.4 million FIRO exist, then a tail emission of 1 FIRO per block. Source (opens in a new tab)
Privacy: what’s hidden, what isn’t
- Privacy model
- optional (user chooses shielded/private)
- What it hides
- For funds in Spark addresses: balances, amounts, the sender and the recipient; Spark addresses cannot be looked up on a block explorer.
- What stays visible
- Transparent address balances and transfers, coins moving between transparent and Spark addresses, mining and masternode rewards, timing and fees; holders can also choose to reveal activity with view keys.
- Reality check
- Firo has replaced or patched its privacy protocol several times after flaws were found: Zerocoin in 2019, and in 2026 a coin-forging bug that Firo traced to the Spark paper itself and that its audits had missed. Spark's strength also depends on users actually moving funds into it. Coinbase and Kraken do not list FIRO, and EU rules cover optional-privacy coins from July 2027.
How Firo works
Firo started as Zcoin, the project that first put the Zerocoin protocol into live use, which worked by burning coins and later redeeming fresh ones with no history. After a 2019 flaw in Zerocoin's proofs let an attacker create coins, the team moved to Sigma, then Lelantus in January 2021, and finally Lelantus Spark in January 2024. Spark uses familiar building blocks such as Pedersen commitments and range proofs and needs no trusted setup.
With Spark, funds sitting in a Spark address are hidden, so outsiders cannot see the balance or when it is spent, and recipients get privacy through a new address format. Owners can share view keys so an accountant or auditor can see incoming or outgoing payments. Transparent addresses still exist, and special exchange addresses that only accept transparent funds were added in response to European MiCA discussions.
Blocks are mined with FiroPoW, a GPU-focused variant of ProgPoW adopted in October 2021 that changes slightly with every block and uses a memory dataset that started at just over 4GB, sized for consumer graphics cards. Masternodes, which lock up FIRO as collateral, form quorums that power ChainLocks, making a block final after one confirmation, and InstantSend for near-instant payments. ChainLocks were rushed into service after the January 2021 attack to block deep chain rewrites.
Key moments
- 2016Zcoin launches, pioneering live use of the Zerocoin privacy protocol.
- 2019In April a cryptographic flaw in Zerocoin is found after an attacker forges coins; Zerocoin is disabled and Sigma replaces it.
- 2020Zcoin rebrands to Firo on November 30, on the same blockchain with no coin swap.
- 2021Lelantus activates in January; days later a 51% attack rolls back over 300 blocks, and ChainLocks go live in response; FiroPoW mining starts in October.
- 2024Lelantus Spark activates in January, and a community vote sets new emission rules from September.
- 2025Spark Names, human-readable aliases for Spark addresses, go live on mainnet on May 28.
- 2026After a researcher privately reports a flaw that could let an attacker forge coins in multi-input Spark spends, Firo limits Spark spends to a single input in August, then restores full spending with a hard fork at block 1,371,000 around September 4. The project says it found no inflation beyond about 200 FIRO the researcher created to prove the bug.
Supply
Since a September 2024 hard fork, Firo issues a fixed 6.25 FIRO per block until supply reaches 21.4 million, then continues with a permanent tail emission of 1 FIRO per block. Each block reward is split 70% to masternodes, 5% to miners, 15% to a development fund and 10% to a community fund. The core team has pledged not to propose further tokenomics changes before tail emission begins.
Risks to understand
- Firo has had serious incidents: a 2019 Zerocoin flaw let coins be forged, a January 2021 51% attack reversed over 300 blocks and cost exchanges money, and in August 2026 the project disclosed a Spark flaw that could allow coin forging, which it blocked with an emergency patch and fixed in a September 2026 hard fork.
- Privacy is optional at the protocol level, so funds held or sent transparently get no protection; use Spark addresses if privacy matters to you.
- Major US exchanges do not list FIRO, and trading happens mostly on smaller exchanges and swap services.
- Masternodes now receive most rewards and power ChainLocks, so security depends heavily on that set of operators.
- From July 10, 2027 the EU's anti-money-laundering regulation bars crypto service providers there from handling coins with optional or default anonymity features.
Firo FAQ
Is Firo the same as Zcoin?
Yes. Zcoin renamed itself Firo in November 2020 and kept the same blockchain, so holders did not need to swap coins.
Are all Firo transactions private?
No. Funds held and sent through Spark addresses are private, but transparent addresses still exist and their activity is public.
Is Firo legal in the US?
As of October 2026 owning FIRO is legal in the US, but Coinbase, Kraken and Robinhood do not list it.
Sources
- Lelantus Spark Binary Release (opens in a new tab) — Firo
- Spark Vulnerability Mitigated (opens in a new tab) — Firo
- Zcoin is becoming Firo (opens in a new tab) — Firo
- Firo 51% attack post mortem and vote on attackers' funds (opens in a new tab) — Firo Forum
- Firo Finalized Tokenomics Results (opens in a new tab) — Firo
- FiroPoW and InstantSend Release with Firo v0.14.9.0 (opens in a new tab) — Firo
- Zerocoin exploit found, Zcoin attacked, other privacy coins at risk (opens in a new tab) — CryptoSlate
- Regulation (EU) 2024/1624 (Anti-Money Laundering Regulation) (opens in a new tab) — EUR-Lex, Official Journal of the EU
Last reviewed October 20, 2026. Written by Dave McNaught. Utility Lens ratings are editorial judgments, not investment advice. Market data from CoinGecko. Spot an error? Request a correction.
Dave McNaught
Dave McNaught has worked in IT since 1999 and founded All Business Technologies (ABT) in 2003, a Boston-area firm providing Managed IT, Cybersecurity, Managed AI, Web Design and App Development. He publishes The Crypto Guide.