Blockchains are a new concern in electronic discovery. The basic technology was developed back in 2008. Its first use was for bitcoins as means to prevent double spending - or the use of a digital token more than once. Timestamped transactions are recorded in a public ledger in such way that they cannot be altered. Data in a blockchain cannot be changed once is is recorded. Blockchains use distributed databases - there are multiple storage devices - not linked to a common processor. So a blockchain is stored on many different computers simultaneously. Each block in the chain has a hash value from the previous block. The integrity of the block chain is confirmed by the network.
IBM, Ernst & Young, KPMG, PwC, and Deloitte are all developing private blockchains. It is also being used to store medical records.