Bitcoin's blockchain contains child abuse images, meaning the cryptocurrency's possession could be 'illegal'

German researchers have analysed more than 1,600 files in the technology required to access the cryptocurrency and found 99 per cent are texts and images, including some illicit pornography and other outlawed content.

It is essentially a public ledger of all the transactions ever made in the currency and keeps a record of which user owns what and stops the coins from being copied.

This is locked and cannot be changed.

However users can leave "non-financial data", the analysis of which has found links and attachments that "contain content to be considered objectionable in many jurisdictions".