Bitcoin (BTC) miner Marathon Digital confirmed that it mined an invalid BTC block at height 809478.

“We can confirm that Marathon did mine an invalid bloc,” Marathon Digital said. “We utilize a small portion of our hash rate to experiment with our development pool and research potential methods to optimize our operations.”

In a Sept. 27 post on X(formerly Twitter), Marathon Digital blamed the invalid block on an unanticipated bug from one of its experiments. According to the miner, its team corrected the invalid block immediately after it was noticed.

It added:

“In no way was this experiment an attempt to alter Bitcoin Core in any way…This incident, while unintended, underscores the robust security of the Bitcoin network, which rejected and rectified the anomaly.”

The miner further assured the community that the bug was unrelated to its production pool and Bitcoin core.

Earlier today, anonymous Bitcoin developer 0xB10C said the miner’s MARAPool had experienced an issue with transaction ordering. The incidence was further confirmed by crypto firm BitMex.

BitMex stated that the invalid mining activity was probably due to the presentation of transactions in the wrong order. According to the firm, the mining company tried initiating a second transaction with the same details as an earlier initiated one.

Meanwhile, CasaHODL co-founder Jameson Lopp described the incident as further evidence that Bitcoin is an impenetrable fortress of validation preventing double-spending. This view was shared by Marathon Digital, which stated, “Bitcoin functioned exactly as designed by excluding the invalid block.”