It looks like one of Bitcoin’s premier mining pools, AntPool, has activated AsicBoost on its mining operations. AsicBoost purportedly increases mining efficiency by up to 20 percent, making its usage very controversial.

There’s a website that tracks just what percentage of Bitcoin BTC blocks are mined using the sneaky new tech. According to AsicBoost Block Explorer, block #540032, mined by AntPool, was actually mined using AsicBoost to gain rewards quicker than usual.

It is worth pointing out this is hardly the first time AntPool has dealt with such criticism.

Indeed, the company was accused of using AsicBoost several times over the last year. The controversy first began when Blockstream CTO Greg Maxwell called out Bitmain, the world’s leading maker of cryptocurrency mining hardware, for using a “mathematical trick” to mine Bitcoin faster than its competitors.

It should be noted that AntPool is directly controlled by Bitmain. Currently, AntPool is the second largest Bitcoin mining pool, representing 13.5 percent of the network. BTC.com (another Bitmain subsidiary) is number one, worth 17.5 percent of Bitcoin’s hash power.

Bitmain repeatedly denies accusations that it developed the technology, claiming to have never used it on the main Bitcoin blockchain. CEO Jihan Wu did, however, acknowledge the company experimented with the technology on a testnet.

Hard Fork has reached out to Bitmain for an official statement, and will update this piece should we receive a reply.

Over the past week, roughly four percent of Bitcoin’s blocks have been mined using AsicBoost. You can track how often it happens here.