Who hacked The DAO in 2016, diverting 3.6 million ether? We identify the apparent hacker — he denies it — by following a complicated trail of crypto transactions and using a previously undisclosed privacy-cracking forensics tool.
Ethereum, the second biggest crypto network, is worth $360 billion. Its creator, Vitalik Buterin, has more than 3 million Twitter followers, has made videos with Ashton Kutcher and Mila Kunis, and has met with Vladimir Putin. All the most popular trends in crypto over the last several years launched on Ethereum: initial coin offerings (ICOs), decentralized finance (DeFi), non-fungible tokens (NFTs), and decentralized autonomous organizations (DAOs). And it has spawned a whole class of blockchain imitators, often called “Ethereum killers.”
Ethereum is also the subject of a great mystery: who committed the largest theft of ether (Ethereum’s native token) ever, by hacking The DAO? The decentralized venture capital fund had raised $139 million in ether (ETH) by the time its crowd sale ended in 2016, making it the most successful crowdfunding effort to that date. Weeks later, a hacker siphoned 31% of the ETH in The DAO—3.64 million total or about 5% of all ETH then outstanding—out of the main DAO and into what became known as the DarkDAO.
Who hacked The DAO? My exclusive investigation, built on the reporting for my new book, The Cryptopians: Idealism, Greed, Lies, and the Making of the First Big Cryptocurrency Craze, appears to point to Toby Hoenisch, a 36-year-old programmer who grew up in Austria and was living in Singapore at the time of the hack. Until now, he has been best known for his role as a cofounder and CEO of TenX, which raised $80 million in a 2017 initial coin offering to build a crypto debit card—an effort that failed. The market cap of those tokens, which spiked at $535 million, now sits at just $11 million.
After being sent a document detailing the evidence pointing to him as the hacker, Hoenisch wrote in an email, “Your statement and conclusion is factually inaccurate.” In that email, Hoenisch offered to provide details refuting our findings—but never answered my repeated follow-up messages to him asking for those details.
To put the enormity of this hack in perspective, with ETH now trading around $3,000, 3.64 million ETH would be worth $11 billion. The DAO theft famously and controversially prompted Ethereum to do a hard fork—where the Ethereum network split into two as a way to restore the stolen funds—which ultimately left the DarkDAO holding not ETH, but far less valuable Ethereum Classic (ETC). The proponents of the fork had hoped ETC would die out, but it now trades around $30. That means the descendant wallets of the DarkDAO now hold more than $100 million in ETC—a high dollar monument to the biggest whodunnit in crypto.
Last year, as I was working on my book, my sources and I, utilizing (among other things), a powerful and previously secret forensics tool from crypto tracing firm Chainalysis, came to believe we had figured out who did it. Indeed, the story of The DAO and the six-year quest to identify the hacker, shows a lot about just how far the crypto world and the technology for tracking transactions have both come since the first crypto craze. Today, blockchain technology has gone mainstream. But as new applications arise, one of the first uses of crypto—as an anonymity shield—is in retreat, thanks to both regulatory pressure and the fact that transactions on public blockchains are traceable.
Since Hoenisch won’t talk to me, I can only speculate about his possible motives; back in 2016 he identified technical vulnerabilities in the DAO early and may have decided to strike after concluding his warnings weren’t being taken seriously enough by the creators of the DAO. (One of his TenX cofounders, Julian Hosp, an Austrian medical doctor who now works in blockchain full time, says of Hoenisch: “He is a person that is super opinionated. Always believed he was right. Always.”) Looked at from that perspective, this is also a tale of the big brains and big egos that drive the crypto world–and of a hacker who may have justified his actions by telling himself he simply did what the faulty code baked into The DAO allowed him to do.
In early 2016, the Ethereum network was not even a year old, and there was only one app on it that people were interested in: The DAO, a decentralized venture fund built with a smart contract that gave its token holders the right to vote on proposals submitted for funding. It had been created by a company named Slock.it, which, instead of seeking traditional venture capital, had decided to create this DAO and then open it up for crowdfunding—with the expectation that its own project would be one of those funded by The DAO. Slock.it’s team thought The DAO might attract $5 million.
Yet when the crowd sale opened on April 30th, it took in $9 million in just the first two days, with participants exchanging one ether for 100 DAO tokens. As the money poured in, some on the team felt queasy, but it was too late to cap the sale. By the time the funding closed a month later, 15,000 to 20,000 individuals had contributed, The DAO held what was then 15% of all ether and the price of the cryptocurrency was steadily rising. At the same time, a variety of security and structural concerns were being raised about The DAO, including one that would, ironically, later prove to be crucial to limiting the hacker’s immediate access to the spoils. That problem: withdrawing funds was too hard. Someone wanting to retrieve their money had to first create a “child DAO” or “split DAO,” which required not only a high degree of technical knowledge, but also waiting periods after each step and the agreement of anyone else who moved funds into that child DAO.
On the morning of June 17th, ETH reached a new all-time high of $21.52, making the crypto in The DAO worth $249.6 million. When American Griff Green woke up that morning in Mittweida, Germany (he was staying in the family home of two brothers who were Slock.it cofounders), he had a message on his phone from a DAO Slack community member who said something weird was happening— it looked like funds were being drained. Green, Slock.it’s first employee and community organizer, checked: there was indeed a stream of 258-ETH (then $5,600) transactions leaving The DAO. By the time the attack stopped a few hours later, 31% of the ETH in The DAO had been siphoned out into the DarkDAO. As awareness of the attack spread, ether had its highest trading day ever, with its price plummeting 33% from $21 to $14.
Soon, the Ethereum community pinpointed the vulnerability that enabled this theft: the DAO smart contract had been written so that any time someone withdrew money, the smart contract would send the money first, before updating that person’s balance. The attacker had used a malicious smart contract that withdrew money (258 ETH at a time), then interfered with the updating of the contract, allowing them to withdraw the same ether again and again. It was as if the attacker had $101 in their bank account, withdrew $100 at a bank, then kept the bank teller from updating the balance to $1, and again requested and received another $100.
Even worse, once the vulnerability became public, the remaining 7.3 million ETH in The DAO was at risk of a copycat attack. A team of white hat hackers (that is, hackers acting ethically) formed and used the attacker’s method to divert the remaining funds into a new child DAO. But the attacker still had about 5% of all outstanding ETH, and even the rescued ether was vulnerable, given the flaws in The DAO. Plus, the clock was ticking down to a July 21st deadline—the first date when the original hacker might be able to get at the funds they had diverted into the DarkDao. If the community wanted to keep the attacker from cashing out, they would need to put tokens in the hacker’s DarkDAO and then in any future “split DAOs” (or child DAOs) the unknown hacker created. (Under the rules of the DAO smart contract, the attacker couldn’t withdraw funds if anyone else in their split DAO objected.) Bottom line: if the white hats ever missed their window to object, the attacker would be able to abscond with the funds—meaning this informal group would have to be constantly vigilant.
Eventually, after much bickering (on Reddit, on a Slack channel, over email and on Skype calls) and Ethereum founder Buterin publicly weighing in, and after it seemed that a majority of the Ethereum community supported the measure, Ethereum did a “hard fork.” On July 20th the Ethereum blockchain was split into two. All the ETH that had been in the DAO was moved to a “withdraw” contract which gave the original contributors the right to send in their DAO tokens and get back ETH on the new blockchain. The old blockchain, which still attracted some supporters and speculators, carried on as Ethereum Classic.
On Ethereum Classic, The DAO and the attacker’s loot (in the form of 3.64 million ETC) remained. That summer, the attacker moved their ETC a few hops away to a new wallet, which remained dormant until late October, when they began trying to use an exchange called ShapeShift to cash the money out to bitcoin. Because ShapeShift didn’t at that time take personally identifying information, the attacker’s identity was not known even though all their blockchain movements were visible. Over the next two months, the hacker managed to obtain 282 bitcoins (then worth $232,000, now more than $11 million). And then, perhaps because ShapeShift frequently blocked their attempted trades, they gave up cashing out, leaving behind 3.4 million Ether Classic (ETC), then worth $3.2 million and now more than $100 million.
That might have been the end of the story—an unknown hacker sitting on a fortune he couldn’t cash out. Except last July, one of my sources involved in the DAO rescue, a Brazilian named Alex Van de Sande (aka Avsa) reached out, saying the Brazilian Police had opened an investigation into the attack on The DAO — and whether he might be a victim or even the hacker himself. Van de Sande decided to commission a forensics report from blockchain analytics company Coinfirm to help exonerate himself (though then, the police closed the investigation, he said). In case any similar situations arose in the future, he went forward with the report examining those cash-out attempts in 2016.
Among the early suspects in the hack had been a Swiss businessman and his associates, and in tracing the funds, Van de Sande and I also found another suspect: a Russia-based Ethereum Classic developer. But all these people were in Europe/Russia and the cash-outs mapped onto an Asian-morning-through-evening schedule—from 9 A.M. to midnight Tokyo time—when the Europeans were likely sleeping. (The timing of their social media posts suggested they kept fairly normal hours.) But based on a customer support email the hacker had submitted to ShapeShift in the leadup to the attack, I believed they spoke fluent English.
Jumping off from the Coinfirm analysis, blockchain analytics company Chainalysis saw the presumed attacker had sent 50 BTC to a Wasabi Wallet, a private desktop Bitcoin wallet that aims to anonymize transactions by mixing several together in a so-called CoinJoin. Using a capability that is being disclosed here for the first time, Chainalysis de-mixed the Wasabi transactions and tracked their output to four exchanges. In a final, crucial step, an employee at one of the exchanges confirmed to one of my sources that the funds were swapped for privacy coin Grin and withdrawn to a Grin node called grin.toby.ai. (Due to exchange privacy policies, normally this sort of customer information would not be disclosed.)
The IP address for that node also hosted Bitcoin Lightning nodes: ln.toby.ai, lnd.ln.toby.ai, etc., and was consistent for over a year; it was not a VPN.
It was hosted on Amazon Singapore. Lightning explorer 1ML showed a node at that IP called TenX.
For anyone who was into crypto in June 2017, this name may ring a bell. That month, as the ICO craze was reaching its initial peak, there was an $80 million ICO named TenX. The CEO and cofounder used the handle @tobyai on AngelList, Betalist, GitHub, Keybase, LinkedIn, Medium, Pinterest, Reddit, StackOverflow, and Twitter. His name was Toby Hoenisch.
Where was he based? In Singapore.
Although he was German-born and raised in Austria, Hoenisch is fluent in English.
The cash-out transactions occurred mainly from 8 A.M. until 11 P.M. Singapore time.
And the email address used on that account at the exchange was [name of exchange]@toby.ai.
In May 2016, as it was finishing up its historic fundraise, Hoenisch was intensely interested in The DAO. On May 12, he emailed Hosp a tip (“Profitable crypto trade coming up”) to short ETH once the DAO crowdfunding period ended. On May 17th and 18th, in the DAO Slack channel, he engaged in a long conversation in which he made, depending on how you count, 52 comments, minimum, about vulnerabilities in The DAO, getting into various aspects of the code and nitpicking over exactly what was possible given the way the code was structured.
One issue spurred him to email Slock.it’s chief technology officer, Christoph Jentzsch, its lead technical engineer, Lefteris Karapetsas, and community manager Griff Green. In his email, he said he was writing a proposal for funding from The DAO for a crypto card product called DAO.PAY, and added, “For our due diligence, we went through the DAO code and found a few things that are worrisome.” He outlined three possible attack vectors and later emailed with a fourth. Jentzsch, a German who had been working on a PhD in physics before dropping out to focus on Ethereum, responded point by point, conceding some of Hoenisch’s assertions but saying others were “false” or “don’t work.” The back and forth ended with Hoenisch writing; “I’ll keep you in the loop if we find anything else.”
But instead of further email exchanges, on May 28th, Hoenish wrote four posts on Medium, beginning with, “TheDAO—risk free voting.” The second, “TheDAO—blackmailing withdrawals,” foreshadowed the main issue with The DAO and why Ethereum ultimately chose to hard fork: if it did not, the only other options were to let the attacker cash out his ill-gotten gains or for some group of DAO token holders to follow him forever into new split DAOs he created as he attempted to cash out. “TLDR: If you end upon in a DAO contract without majority voting power, then an attacker can block all withdrawals indefinitely,” he wrote. The third showed how an attacker could do this cheaply.
To put the enormity of this hack in perspective, with ETH now trading around $3,000, 3.64 million ETH would be worth $11 billion.
His last, most telling post for the day, “TheDAO—a $150m lesson in decentralized governance,” said DAO.PAY decided against making a proposal after uncovering “major security flaws” and that “Slockit down-played the severity of the attack vectors.” He wrote, “TheDAO is live … and we are still waiting for Slockit to put out a warning that THERE IS NO SAFE WAY TO WITHDRAW!”
On June 3, his last Medium post, “Announcing BlockOps: Blockchain Hack Challenges” said, “BlockOps is your playground to break encryption, steal bitcoin, break smart contracts and simply test your security knowledge.” Although he promised to “post new challenges in the field of bitcoin, ethereum and web security every 2 weeks,” I could find no record that he did so.
Two weeks later came the DAO attack. The morning after the attack, at 7:18 A.M. Singapore time, Hoenisch trolled Ethereum creator Vitalik Buterin by retweeting something Buterin had said before The DAO was attacked, but after it was known that the vulnerability used in the attack was evident in the DAO’s code. In the two-week old tweet, Buterin had said that he’d been buying DAO tokens since the security news. Over the following weeks, Hoenisch tweeted anti-hard fork posts like one titled, “Too Big to Fail is Failure Guaranteed.”
Curiously, on July 5, a couple weeks after the attack, Hoenisch and Karapetsas exchanged Reddit DMs titled “DarkDAO counter attack” — though the substance of the messages is unclear because Hoensich has deleted all his Reddit posts. (Hosp recalls that Hoenisch told him he had deleted his Reddit account after an altercation with an “idiot” on Reddit over The DAO.) Hoenisch wrote, “Sorry for not contacting first. I got carried away from finding it and telling the community that there is a way to fight back. In any case, I don't see any way the attacker can use this.”
After Karapetsas told Hoenisch of the white hats’ plans to protect what was left in The DAO, Hoenisch replied, “I took down the post.” Karapetsas responded, “I will keep you up to date with what we do from now on.” Hoenisch’s last message in that exchange: “I’m sorry if I messed up the plan.”
On July 24th, the day after the Ethereum Classic chain revived and began trading on Poloniex, Hoenisch tweeted, “ethereum drama escalating: from #daowars to #chainwars. Ethereum classic now traded on poloniex as $ETC and miners planning attacks.” On July 26th, he retweeted Barry Silbert, the founder and CEO of the powerful and well-respected Digital Currency Group, who had tweeted, “Bought my first non-bitcoin digital currency…Ethereum Classic (ETC).”
“He (the DAO hacker) really screwed the pooch. Reputation is way more valuable than money.”
Upon hearing the name Toby Hoenisch, without knowing evidence indicated he was the DAO attacker, Karapetsas, a usually good-humored Greek software developer who was one of the DAO creators and had engaged with him by email and on Reddit, said: “He was obnoxious…. he was quite insistent on having found a lot of problems.” After hearing that the DarkDAO ETC had been cashed out to a Grin node with Hoenisch’s alias, Karapetsas observed that if Hoenisch had instead remedied the situation while the DarkDao funds were frozen, the Ethereum community would have given him “huge kudos'' for finding the weakness and then returning the ETH. Similarly, Griff Green, whose current projects lean towards helping non-profit and public causes grow in the digital world, believes the hacker missed the chance to “be a hero.” Says Green: “He really screwed the pooch...Reputation is way more valuable than money.”
Ironically, in a 2016 blog post, Hoenisch wrote, “I’m a white hat hacker by heart.’’ Twenty days later came the DAO attack.
As I noted earlier, after being sent a document laying out the evidence that he was the hacker and asking for comment for my book, Hoenisch wrote that my conclusion is “factually inaccurate.” He said in that email he could give me more details—and then did not respond to four requests for those details, nor to additional fact checking queries for this article. In addition, after receiving the first document detailing the facts I’d gathered, he deleted almost all his Twitter history (though I’ve saved the relevant tweets).
In May 2015, Hoenisch and the cofounders of his crypto debit card venture—first known as OneBit—had some success at a Mastercard Masters of Code hackathon in Singapore. They started making the card available that year on an invitation-only basis, because, as Hoenisch explained on Reddit, “We don’t want to launch a half-assed Bitcoin wallet that gets us in trouble for violating KYC (know your customer) laws. And yes, legal is the main reason we can’t just ship it.” A Bitcoin Magazine article at the time said Hoenisch had a background in AI, IT security and cryptography.
In early 2017, just months after the presumed DAO attacker stopped trying to cash out their ETC, Hoenisch’s team—by then operating as TenX—announced it had received $1 million in seed funding from (among others) Fenbushi Capital, where Ethereum founder Buterin was a general partner. Then came the $80 million ICO. In early 2018, things started to go south for TenX when its card issuer, Wavecrest, was booted from the Visa network, meaning that TenX's users could no longer use their debit cards.
On Oct. 1, 2020, TenX announced it was sunsetting its services because its new card issuer, Wirecard SG, had been directed by the Monetary Authority of Singapore to cease operations. On April 9, 2021, TenX posted a blog called “TenX, Meet Mimo.” It outlined a new business that would offer a euro-pegged stablecoin, which kept its value pegged to a fiat currency such as US dollars or euros or Japanese Yen. The market cap of TenX tokens, which spiked at $535 million, now sits at just $11 million. TenX has rebranded itself as Mimo Capital and is offering holders of TenX tokens mostly worthless MIMO tokens instead at a rate of 0.37 MIMO for each TenX.
Hosp, who was the public face of the company while there, was booted by Hoenisch and another cofounder in January 2019. This occurred a couple months after some crypto publications reported on Hosp’s past affiliation with an Austrian multi-level marketing scheme. However, before hearing that evidence indicated Hoenisch was the DAO attacker, Hosp said his feeling had been that Hoenisch had perhaps pushed him out over jealousy that Hosp had sold bitcoin at the top of the bubble in late 2017, netting himself $20 million. Meanwhile, Hoenisch had kept all his crypto as the bubble – and his personal net worth – deflated.
“He came from a very poor family, he had no experience in investing, and he was in crypto in 2010 but he had literally no money, nothing, when we were in Las Vegas together [in the summer of 2016] he had nothing, and I was doing really well with my investments… he would always push for getting more salary, for having something nicer.” Hosp also mentioned Hoenisch had to send money home to his mother, who had raised him, as well as his sister and brother, as a single parent.
As new blockchain applications arise, one of the first uses of crypto—as an anonymity shield—is in retreat.
Upon hearing that Hoenisch was the likely DAO attacker, Hosp said he was “getting goose bumps” and begin recalling details from his interactions with his former partner that now seemed to take on new significance. For example, when asked if Hoenisch was into Grin (the privacy coins to which the hacker had cashed out) Hosp said, “Yes! Yes, he was. He was fascinated by that…I lost money because of those stupid coins! I invested in them because of him, because he was so fascinated by them.” He said that Hoenisch was also obsessed with building a Bitcoin/Monero “atomic swap” – or a way to use smart contracts to swap between Bitcoin and the privacy coin Monero. At the time, Hosp was confused by that, because he felt there was no market for such a product. Later, Hosp pulled up chats from August 2016, in which Hoenisch seemed excited about the price of ETC, the coin held by the hacker after the ethereum fork.
When trying to recall the incident that he believed prompted Hoenisch to close his Reddit, Hosp began searching on his computer and muttered to himself, “He always used tobyai.” He confirmed that one of Toby’s regular email addresses ended in @toby.ai.
Recalled a still astounded Hosp: “For some weird reason, he was quite well aware of what was happening…He understood more of the DAO hack when I asked him what had happened…than I had found on the internet or anywhere.”