The researcher Loik Morel discovered a computational error in the mechanism of adjusting Bitcoin’s complexity, which had been present since the launch of the network. Bug is related to the calculation of intervals between blocks: when recalculating complexity, each 2016 block node measures the time between the first and last block of period, while actually between them 2015 gaps, not 2016. This 0.05% error results in a slightly exaggerated complexity and, more critically, creates gaps between adjustment periods.

The intruder, controlling a significant share of the hash, could manipulate time stamps: set minimum values for most blocks and maximum for the latter. By repeating the cycle, it can artificially lower the complexity to a level where blocks are generated every 0.16 seconds instead of the usual ten minutes. This would threaten to overload the network, devalue the receipts and capture the reward by blocks.

Morel proposed to eliminate the vulnerability via software in BIP-0054 by limiting the mark difference between the first block of the new period and the last block of the previous two hours. Such a measure restores continuity and blocks the attack of the «flash of time».