Mining pools controlled by the largest Chinese ASIC miners producer Bitmain, mined more than 42% of bitcoin blocks last week, and their share in the network hashrate is growing, making a '51% attack' on bitcoin more real.

According to CoinDance, the mining pools BTC.com and Antpool, controlled by Bitmain, mined 25.5% and 16.5% of bitcoin blocks in the last seven days, respectively. Given that both of these mining pools are owned by Bitmain, the world's largest manufacturer of integrated circuits for mining, Bitmain now controls at least 42% of the bitcoin hashrate. Both pools also have a high production level in the Bitcoin Cash network, accounting for 21.3% of the blocks found.

42% is a level dangerously close to controlling 51% of the bitcoin hashrate, which will allow Bitmain to theoretically attack the bitcoin network in its own interests. Recently, similar attacks using ASIC-miners from Bitmain were successfully deployed against a group of small altcoins, such as Bitcoin Gold, Verge, Litecoin Cash and Monacoin.

It is possible that Bitmain will manage to overcome the threshold of 51% in the coming months, since Antpool recently launched an advertising campaign, offering zero commissions to its new users.

Earlier Cobra, bitcoin-enthusiast and bitcoin.org owner, accused Bitmain of gaining control of over 80% of the bitcoin hashrate.

Concerns about bitcoin network centralization prompted Bitcoin Core developer Matt Corallo to create a BetterHash solution that changes the current bitcoin mining protocol to two new ones. They will allow individual miners to create their own block templates (or take them from a third party) rather than using those offered by pool operators.