Alice, being the curious programmer that she is, decides to write some code on her own computer which is somewhat like a Steem blockchain node, except that certain accounts are no longer recognized.
She runs this node for a while and all is well until, soon enough, one of those unrecognized accounts performs an operation and her node rejects that block as well as any blocks thereafter. Other nodes sending those blocks are recognized as invalid or malicious and are disconnected.
As it turns out, Alice is a witness on the network and has configured her node to require a minimum participation of zero. As such, her witness continues to sign blocks, and the other witness accounts present on her computer continue to miss blocks until the blockchain code eventually disables them. Alice is able to vote in her own group of 20 top witness accounts and her node functions perfectly (except, of course, that no one else is using it). Perhaps Alice uses this node for experimental or development purposes or, you know, "self amusement". It doesn't matter which.
One day, Alice is talking to her friend Bob and telling him about this node of hers when it occurs to Bob, "You know, I have an account on that node, since I had an account on Steem [not one of the ones Alice disabled]. It would be fun if you gave me your modified version of the code, I connected my node to your node and we could then amuse each other." So they did.
Soon, Alice and Bob invited their friend Charlie to join the party and things really got going. In time, half of Steem's users joined up, and soon thereafter more than half. Eventually, nearly all of Steem's users were connected to each other using Alice's modifications, all were happy and and all sorts of varied amusement took place. So much so, in fact, that the old blockchain fell into disuse. Still there, of course, as it is nearly impossible to fully destroy a blockchain, but no one much cared about it any more.
Theft? Piracy? Heist? Hackers? Violating property rights?
You decide.
