Bitcoin Forum

I believe the attach never took place.  However, I0coin & Ixcoin supposedly were attacked which is why the bitparking exchanges for these coins were shut down.

The ideas behind the "attacks" includes spamming transactions between addresses verified by more than 50% processing power (b/c you own more than 50%). 

If you're looking for specifics of how to do this, why????

I'm surveying all known vulnerabilities of bitcoin and related protocols.  I have no evil designs. :)

That's fair.  I agree that we should assume anything that can be done, will be done.  So we need to not rely on people "doing the right thing" but rather focusing on how to just be ready for anything to happen.

That's life in an unregulated decentralized world.  You get both the ups and the downs.

From what I remember the  threatened attacks at the time were:

• Namecoin had a low hash rate. The attacker had >51% of the rate. use the 'timewarp/zeitgeist' exploit that ArtForZ discovered on the GeistGeld chain to mine blocks at low difficulty to obtain a large number of coins quickly.
• With >51% of the hash rate, rewrite the namecoin blockchain since there was no recent checkpoint at the time.
• The attacker claimed to know of an exploit involving merged mining that would enable them to 'leapfrog' checkpoints and rewrite the chain with a hash rate less than 50%.

The bitparking i0coin exchange was the victim of a >51% attack on the chain whereby the attacker would deposit, trade for bitcoins and then release a fork of the chain with the deposit transaction invalidated. This is why I closed the exchange. The ixcoin exchange was never attacked (to my knowledge) but I closed it as well since it also had a low hash rate and could suffer a similar attack.

Yep, I agree with your call.  Can't run an exchange with such a vulnerable chain. :(

The NMC exploit should not be viable, because it has a lot more hash power now with merged mining.

Thanks, everyone.  That gave me enough information to hunt down the history.  It is outlined in more detail here (http://bitcoin.stackexchange.com/questions/1023/why-did-bitcoinexpress-plann-a-51-attack-on-namecoin).

Exactly. Today one would need ~3TH or almost 100x as much hashing power to pull off the exploit.  In time I expect almost every pool to offer merged mining so namecoin network power will continue to rise closer to BTC.  Never 100% but maybe 80%+ is possible.  Even if BTC's hashing power  declined fell to ~5TH (which I think is likely over the next year) that puts NMC in the 4TH range.

declined to?