Marathon Digital Holdings (MARA), a prominent Bitcoin mining company, has reportedly mined an invalid Bitcoin block at height 809478.

According to various developers, miners, and researchers, the invalid Bitcoin block resulted from a wrong transaction ordering.

Anonymous Developer Exposes Transaction Ordering Issue

The issue was first brought to light by an anonymous Bitcoin developer known as 0xB10C, who took to social media platform X to report the incident. According to the developer, the problem originated from a transaction ordering issue within Marathon’s mining pool, known as MaraPool.

“It seems like MARAPool had a transaction ordering issue,” 0xB10C stated in their initial tweet. They then pinpointed the specific transaction that caused the problem. The invalid block contained a transaction identified as the sixth one in the invalid block. This one attempted to spend an output from another transaction, which was the 1,454th transaction in the block.

Confirmed on my nodes. https://t.co/NIrNMGHnwa

— Jameson Lopp (@lopp) September 27, 2023

Notably, the latter transaction was positioned lower down in the block, invalidating the entire block due to improper transaction ordering.

Furthermore, the developer suggested that Marathon Digital might have been running custom code. They stated, “They might be running custom code. Bitcoin Core normally double-checks block validity after creating a block template,” hinting at the possibility of a customized approach that deviated from established practices.

Lopp and BitMEX Confirm Invalid Bitcoin Block Incident

Jameson Lopp, the co-founder of CasaHODL, also weighed in on the matter, responding by confirming this claim.

Confirmed on my nodes. https://t.co/NIrNM