Images of child sexual abuse have been found embedded in the system powering a high-profile crypto-currency.
Somebody added the illegal images to the core ledger of Bitcoin Satoshi Vision (BSV) by using a payment processor.
This ledger, known as the blockchain, is a running record of crypto-currency transactions, shared among users of the platform.
Experts have warned that abuse of blockchain tech is a growing problem.
The blockchain is central to the way many crypto-currencies such as Bitcoin work and in theory stops people making fake transactions or manipulating their account balance.
One key feature of the blockchain is that information added to it cannot be changed without significant effort.
In January, the amount of data that could be added to the BSV blockchain was increased significantly.
Before that, people could generally add only short chunks of text or web links to the blockchain.