http://www.abc.net.au/news/2018-03-21/bitcoins-blockchain-has-bee...

http://www.abc.net.au/news/2018-03-...-has-been-linked-to-child-pornography/9571384

This hasn’t been widely circulated or dissected as yet, however I would regard this as the most significant matter that the Bitcoin blockchain has ever faced.

In short, those in the possession of the BTC chain could find themselves being pursued for illegally storing child pornography.

And the chain maintainers are stuck:

1) Its hard to act in a co-ordinated manner due to the decentralized nature of the chain (ie no one has complete control, so it takes a lot of cooperation with sometimes hostile actors to make changes) and,

2) The changes cannot be made instantly and/or unilaterally: if they could do both of these, then it would become quickly apparent that the blockchain is not truly immutable.

It’s going to be interesting to see how this is overcome.