Bitcoin miner Marathon mines invalid block in failed ‘experiment’

Bitcoin mining firm Marathon Digital has confirmed it mined an invalid  Bitcoin (BTC) block during an “experiment” aimed at optimizing the firm’s operations.

In a Sept. 27 post, Marathon said it utilizes a small percentage of the firm’s hashrate toward these experiments and stressed they weren’t trying to alter the network in any way:

“In no way was this experiment an attempt to alter Bitcoin Core in any way.” Marathon said, emphasizing that they corrected the error as soon as they noticed the invalid block.

We can confirm that Marathon did mine an invalid block. We utilize a small portion of our hash rate to experiment with our development pool and research potential methods to optimize our operations. The error was the result of an unanticipated bug that came from one of our…

— Marathon Digital Holdings (NASDAQ: MARA) (@MarathonDH) September 27, 2023

Marathon said the bug, which emanated from the firm’s internal development environment, wasn’t related to Marathon’s Bitcoin production pool or Bitcoin Core — the leading software used to connect to the Bitcoin network and run a node.

The incident occurred on Sept. 26 at 9:42 pm UTC on block 809478, according to

Several Bitcoin developers, along with BitMEX Research attributed the invalid block to a “transaction ordering issue.” Bitcoin developer “mononaut” believes Marathon mistake came from resorting the transactions in order of ascending absolute fees.

This is what MARA’s invalid block at 809478 looks like:

– pink transactions no longer exist in the main chain
– blue transactions are invalid due to ordering (they spend an output from a transaction included later in the block)

— mononaut (@mononautical) September 27, 2023

Bitcoin analyst Dylan LeClair suggested that Marathon should have conducted this experiment on a testnet before attempting it on Bitcoin’s mainnet.

In reflection, Marathon said Bitcoin “functioned exactly as designed” by excluding the invalid block:

“This incident, while unintended, underscores the robust security of the Bitcoin network,…..


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