This rings a bell, the past illegal contents in the blockchain issue can be linked to that "
OP_Return" function.
I don't know how it works but based on your statement, it is possible to insert "
something" in to the blockchain.
that
something is a 40 bytes of data. it can be anything. a string for example, some secret hashed data,....
P.S: There's a link below the page which said "You can also embed data into the Bitcoin blockchain" which I suspect that is "OP_Return", anyone can confirm this?
the bitcoin network option for it doesn't work since it is not free to send a transaction like that on bitcoin network but you can change it to testnet and send a transaction containing some arbitrary data. it is the Blockcypher bitcoin testnet and it is Op_return
https://live.blockcypher.com/bcy/tx/634aa69a721c7158b03e53037402d31a34f0125befee53275bb59ee7002a6a02/