I'm not sure this has been reported here before. If it has, let me know, I'll lock the topic.
I've been receiving this email once per day lately, sent by
noreply@okura.nl"Hydro Protocol is forking 0x and distributing the new HYD token to ZRX holders
...
To claim HYD tokens, community members must first register on our website, provide a valid Ethereum address and receive 1:1 for the total ZRX balance contained by the registered address.
Tokens can be unlocked immediately through Hydro Webwallet - an easy, safe and user-friendly interface to interact with the Ethereum blockchain."
And of course, to claim your tokens, you have to provide your private key.
