The OmniCoin dev team is glad to announce that Omnicoin is now back online. The pools, exchanges, payment processors, etc should be coming back online shortly. It is also safe to now make transactions with OMC.
What Happened
An attacker, who's identity is unknown, performed what is known as a 51% double spend attack. This attack allows them to send Omnicoin to another party, and then later reverse the transaction by essentially rewriting the blockchain. This is not a fault in Omnicoin itself, it is a fault in all POW cryptocurrencies (including BitCoin).
The attacker sent approximately 1.2 million OMC to AllCrypt.com over the course of 6 transactions. After the deposits had reached 6 confirmations, he reversed the transactions on the blockchain, essentially giving himself back the OMC, while still keeping his account balance on AllCrypt. Then he proceeded to sell approximately 200,000 OMC, totally around 2 BTC, which he withdrew.
What We Did
We decided that this type of attack would be too hard to of a hit for Omnicoin and it would be worth it to do a rollback. Instead of a typical hard forking rollback requiring a client update, we used the exact same method the attacker used to rewrite the blockchain. We rewrote the blockchain starting 1 block before the attacker first showed his face, essentially removing and trace of the attack and taking all the OMC back.
What This Means
Just like the attackers attack had side effects (stolen OMC), our rollback will have side effects of its own. All transaction that were made after block 146197 (15-02-09 22:05:05 CST) will be invalidated. Some transactions will resend themselves in new blocks, but some wont.
What Happened
An attacker, who's identity is unknown, performed what is known as a 51% double spend attack. This attack allows them to send Omnicoin to another party, and then later reverse the transaction by essentially rewriting the blockchain. This is not a fault in Omnicoin itself, it is a fault in all POW cryptocurrencies (including BitCoin).
The attacker sent approximately 1.2 million OMC to AllCrypt.com over the course of 6 transactions. After the deposits had reached 6 confirmations, he reversed the transactions on the blockchain, essentially giving himself back the OMC, while still keeping his account balance on AllCrypt. Then he proceeded to sell approximately 200,000 OMC, totally around 2 BTC, which he withdrew.
What We Did
We decided that this type of attack would be too hard to of a hit for Omnicoin and it would be worth it to do a rollback. Instead of a typical hard forking rollback requiring a client update, we used the exact same method the attacker used to rewrite the blockchain. We rewrote the blockchain starting 1 block before the attacker first showed his face, essentially removing and trace of the attack and taking all the OMC back.
What This Means
Just like the attackers attack had side effects (stolen OMC), our rollback will have side effects of its own. All transaction that were made after block 146197 (15-02-09 22:05:05 CST) will be invalidated. Some transactions will resend themselves in new blocks, but some wont.
![[Image: eeGL95b.gif]](https://i.imgur.com/eeGL95b.gif)
