Evan claims a KGW exploit was deployed against DRK.

The descriptions of the theory of such an exploit explain the difficulty can be reduced quickly by setting the timestamp of the latest block far into the future for the secret chain so the secret chain is mined with much lower difficulty, and then the secret chain can be brought back to the present time before publishing it, because timestamps that walk backwards in time aren't fully counted.

To compute the relative PoW of a chain, sum the modular additive inverse of each hash (e.g. hash subtracted from 2²⁵⁶). The secret chain can't end up with more blocks thus has a lower sum and isn't chosen as the longest chain. Or what appears to be more correct (what that thread is alleging) is if the longest chain is chosen by the greater number of blocks, the secret chain can mine more blocks since it is at a lower difficulty. The key is being able to mine faster at a lower difficulty by being able to move forward and then backward in time asymmetrically.

KGW offers other vulnerabilities because the secret chain can drop the difficulty, then mine faster without causing a rise of difficulty for up a day or so, by staying under the exponential well trigger threshold.

Clearly you see now the potential problem in Cryptonote with the 20% discard rule. It enables the secret chain to hide a bunch of fast blocks (bunching them together in time) without causing a rise in difficulty. Thus the secret chain can end up the longest chain without needing 50% of the hashrate.

I now change my opinion to very likely that BCX is building a secret chain nowRescinded. How many more days to the 22 day countdown?