<p>As I understand it (and wrote at more length in <a href="https://bitcoin.stackexchange.com/questions/22104/wouldnt-the-malleable-transaction-attack-be-foiled-by-common-sense">this question</a>), the statement is technically correct but incomplete.</p>

<p>The result of a malleable transaction attack is that the targeted transaction (in which the victim voluntarily sent coins to the attacker) does not confirm, but an equivalent transaction with a different ID does confirm.  It is true that this does not steal any coins: the recipient gets the same coins they were already getting.</p>

<p>The theft occurs in the next step, not described in your statement: the attacker points out to the victim that the original transaction didn't confirm, and convinces him to resend the amount, in a new and independent transaction.  If the victim doesn't notice the attacker's equivalent transaction, he might do this; then the attacker has received twice as many coins as he was supposed to.</p>

CC BY-SA 3.0
2014-03-01T02:15:40.973Z
i.e. if malleability was the issue, mtGox would have been dealing with a large volume of support calls, or their wallet was doing this automatically
alfwatt
CC BY-SA 3.0
2014-05-22T17:01:59.193Z
@Nate, so you are saying that MtGox is plain lying when they claim that it is a DOS attack?
Pacerier
CC BY-SA 3.0
2014-05-22T17:07:41.850Z
@Pacerier: I am not aware that MtGox has made any such claim.  The statement quoted above is attributed to gavin of the Bitcoin Foundation, who as far as I know is not affiliated with MtGox.
Nate Eldredge
CC BY-SA 3.0
2014-02-26T17:25:30.543Z
2014-02-26T17:25:30.543Z
2017-04-13T12:47:33.610Z
Nate Eldredge
<blockquote>
  <p><strong>Were bitcoins actually stolen</strong></p>
</blockquote>

<p>Almost certainly yes.</p>

<p><strong>Update</strong> (March 21 2014): 200,000 bitcoin were found recently <a href="http://www.theregister.co.uk/2014/03/21/mtgox_finds_200000_bitcoin_in_old_wallets/" rel="nofollow">down the back of an old MtGox sofa (more or less)</a> So some of the bitcoins might have been merely carelessly mislaid. No one has suggested that these bitcoins may have been deliberately hidden by an insider for later retrieval. So far it's reported as incompetence rather than criminal theft. That still leaves a much larger number of bitcoins that currently appear to have been stolen.</p>

<p>Forbes <a href="http://www.forbes.com/sites/cameronkeng/2014/02/25/bitcoins-mt-gox-shuts-down-loses-409200000-dollars-recovery-steps-and-taking-your-tax-losses/" rel="nofollow">reports</a></p>

<blockquote>
  <p>The company’s shutdown is rumored to be caused by a “hack” or “security breach” that resulted in a loss up to 744,000 BTC or $409,200,000. </p>
</blockquote>

<p>The BBC <a href="http://www.bbc.co.uk/news/technology-26352442" rel="nofollow">reports</a></p>

<blockquote>
  <p>An estimated 744,000 bitcoins - about $350m (£210m) - are believed to have been <strong>stolen</strong> thanks to a loophole in Tokyo-based MtGox's security.<br>
  ...<br>
  A leaked report - which Mr Karpeles has confirmed is authentic - said the huge theft had made MtGox insolvent.</p>
</blockquote>

<p>The <a href="http://www.scribd.com/doc/209050732/MtGox-Situation-Crisis-Strategy-Draft" rel="nofollow">leaked report referred to</a>  says</p>

<blockquote>
  <p>At this point 744,408 BTC are missing due to malleability-related <strong>theft</strong> which went unnoticed for several years. The cold storage has been wiped out due to a leak in the hot wallet<br>
  ...<br>
  MtGox's main problems are massive <strong>robbery</strong> and poor bitcoin accounting.</p>
</blockquote>

<hr>

<p>Yahoo news <a href="http://news.yahoo.com/tokyo-bitcoin-exchange-files-bankruptcy-102841684--finance.html" rel="nofollow">reports</a> (on 2014-02-28)</p>

<blockquote>
  <p>CEO Mark Karpeles appeared before Japanese TV news cameras, bowing deeply. He said a weakness in the exchange's systems was behind a massive loss of the virtual currency involving 750,000 bitcoins from users and 100,000 of the company's own bitcoins. That would amount to about $425 million at recent prices.<br>
  ...<br>
  It remains unclear if the missing bitcoins were <strong>stolen, voided by technological flaws or both</strong>.</p>
</blockquote>

<p>Bloomberg <a href="http://www.bloomberg.com/news/2014-02-28/mt-gox-exchange-files-for-bankruptcy.html" rel="nofollow">reports</a></p>

<blockquote>
  <p>“The company believes there is a high possibility that the Bitcoins were <strong>stolen</strong>,” Mt. Gox said in a statement.</p>
</blockquote>

CC BY-SA 3.0
2014-02-27T19:52:18.633Z
Then what does this mean?  "This is a denial-of-service attack; whoever is doing this is not stealing coins, but is succeeding in preventing some transactions from confirming. It’s important to note that DoS attacks do not affect people’s bitcoin wallets or funds."
Keshav Srinivasan
CC BY-SA 3.0
2014-02-27T20:20:42.067Z
@Keshav: That's what Gavin Andresen thought was the case on [Feb 11](https://bitcoinfoundation.org/blog/?p=422). The sources I quoted are from more than two weeks later.
RedGrittyBrick
CC BY-SA 3.0
2014-02-27T14:56:18.853Z
2014-03-21T11:32:33.777Z
2014-03-21T11:32:33.777Z
RedGrittyBrick
<p>What's being reported on the news is that millions of Bitcoins were stolen from Mt Gox.  But the Bitcoin Foundation blog says something different:</p>

<p><a href="https://bitcoinfoundation.org/blog/?p=422" rel="nofollow">https://bitcoinfoundation.org/blog/?p=422</a></p>

<blockquote>
  <p>"Somebody (or several somebodies) is taking advantage of the transaction malleability issue and relaying mutated versions of transactions. This is exposing bugs in both the reference implementation and some exchange’s software.</p>
  
  <p>We (core dev team, developers at the exchanges, and even big mining pools) are creating workarounds and fixes right now. This is a denial-of-service attack; whoever is doing this is not stealing coins, but is succeeding in preventing some transactions from confirming. It’s important to note that DoS attacks do not affect people’s bitcoin wallets or funds."</p>
</blockquote>

<p>So is the transaction malleability issue Mt Gox is suffering from just a denial-of-service attack, or were Bitcoins actually stolen?</p>

<p>Any help would be greatly appreciated.</p>

<p>Thank You in Advance.</p>

CC BY-SA 3.0
2014-02-27T06:38:52.927Z
The two statements are talking about two completely different events. The only thing they have in common is that they are both caused by transaction malleability. One is inherent in Bitcoin's design, the other is specific to Mt Gox.
David Schwartz
<security><mtgox><transaction-malleability>
Does the Mt Gox attack constitute theft of Bitcoins or just a Denial-of-Service attack?
Keshav Srinivasan
# Does the Mt Gox attack constitute theft of Bitcoins or just a Denial-of-Service attack?

(Asked by: username_0 on 2014-02-26)

What's being reported on the news is that millions of Bitcoins were stolen from Mt Gox. But the Bitcoin Foundation blog says something different:

<https://bitcoinfoundation.org/blog/?p=422>

> "Somebody (or several somebodies) is taking advantage of the transaction malleability issue and relaying mutated versions of transactions. This is exposing bugs in both the reference implementation and some exchange’s software.
>
> We (core dev team, developers at the exchanges, and even big mining pools) are creating workarounds and fixes right now. This is a denial-of-service attack; whoever is doing this is not stealing coins, but is succeeding in preventing some transactions from confirming. It’s important to note that DoS attacks do not affect people’s bitcoin wallets or funds."

So is the transaction malleability issue Mt Gox is suffering from just a denial-of-service attack, or were Bitcoins actually stolen?

Any help would be greatly appreciated.

Thank You in Advance.

**Tags:** security, mtgox, transaction-malleability

> **Comments:**
> **username_1**: The two statements are talking about two completely different events. The only thing they have in common is that they are both caused by transaction malleability. One is inherent in Bitcoin's design, the other is specific to Mt Gox.  

---

## 2 answers

### Answer by username_2 on 2014-02-26. Score: 3

As I understand it (and wrote at more length in [this question](https://bitcoin.stackexchange.com/questions/22104/wouldnt-the-malleable-transaction-attack-be-foiled-by-common-sense)), the statement is technically correct but incomplete.

The result of a malleable transaction attack is that the targeted transaction (in which the victim voluntarily sent coins to the attacker) does not confirm, but an equivalent transaction with a different ID does confirm. It is true that this does not steal any coins: the recipient gets the same coins they were already getting.

The theft occurs in the next step, not described in your statement: the attacker points out to the victim that the original transaction didn't confirm, and convinces him to resend the amount, in a new and independent transaction. If the victim doesn't notice the attacker's equivalent transaction, he might do this; then the attacker has received twice as many coins as he was supposed to.

> **Comments:**
> **username_3**: i.e. if malleability was the issue, mtGox would have been dealing with a large volume of support calls, or their wallet was doing this automatically  
> **username_4**: @username_2, so you are saying that MtGox is plain lying when they claim that it is a DOS attack?  
> **username_2**: @username_4: I am not aware that MtGox has made any such claim.  The statement quoted above is attributed to gavin of the Bitcoin Foundation, who as far as I know is not affiliated with MtGox.  

---

### Answer by username_5 on 2014-02-27. Score: 1

> **Were bitcoins actually stolen**

Almost certainly yes.

**Update** (March 21 2014): 200,000 bitcoin were found recently [down the back of an old MtGox sofa (more or less)](http://www.theregister.co.uk/2014/03/21/mtgox_finds_200000_bitcoin_in_old_wallets/) So some of the bitcoins might have been merely carelessly mislaid. No one has suggested that these bitcoins may have been deliberately hidden by an insider for later retrieval. So far it's reported as incompetence rather than criminal theft. That still leaves a much larger number of bitcoins that currently appear to have been stolen.

Forbes [reports](http://www.forbes.com/sites/cameronkeng/2014/02/25/bitcoins-mt-gox-shuts-down-loses-409200000-dollars-recovery-steps-and-taking-your-tax-losses/)

> The company’s shutdown is rumored to be caused by a “hack” or “security breach” that resulted in a loss up to 744,000 BTC or $409,200,000.

The BBC [reports](http://www.bbc.co.uk/news/technology-26352442)

> An estimated 744,000 bitcoins - about $350m (£210m) - are believed to have been **stolen** thanks to a loophole in Tokyo-based MtGox's security.  
> ...  
> A leaked report - which Mr Karpeles has confirmed is authentic - said the huge theft had made MtGox insolvent.

The [leaked report referred to](http://www.scribd.com/doc/209050732/MtGox-Situation-Crisis-Strategy-Draft) says

> At this point 744,408 BTC are missing due to malleability-related **theft** which went unnoticed for several years. The cold storage has been wiped out due to a leak in the hot wallet  
> ...  
> MtGox's main problems are massive **robbery** and poor bitcoin accounting.

---

Yahoo news [reports](http://news.yahoo.com/tokyo-bitcoin-exchange-files-bankruptcy-102841684--finance.html) (on 2014-02-28)

> CEO Mark Karpeles appeared before Japanese TV news cameras, bowing deeply. He said a weakness in the exchange's systems was behind a massive loss of the virtual currency involving 750,000 bitcoins from users and 100,000 of the company's own bitcoins. That would amount to about $425 million at recent prices.  
> ...  
> It remains unclear if the missing bitcoins were **stolen, voided by technological flaws or both**.

Bloomberg [reports](http://www.bloomberg.com/news/2014-02-28/mt-gox-exchange-files-for-bankruptcy.html)

> “The company believes there is a high possibility that the Bitcoins were **stolen**,” Mt. Gox said in a statement.

> **Comments:**
> **username_0**: Then what does this mean?  "This is a denial-of-service attack; whoever is doing this is not stealing coins, but is succeeding in preventing some transactions from confirming. It’s important to note that DoS attacks do not affect people’s bitcoin wallets or funds."  
> **username_5**: @username_0: That's what Gavin Andresen thought was the case on [Feb 11](https://bitcoinfoundation.org/blog/?p=422). The sources I quoted are from more than two weeks later.  

---

