It's down for upgrade at the moment. What prevents immutable spam?

Back up! - nothing! it's completely open. You can only make a post when there are no other pending messages waiting to be confirmed in the Bitcoin Blockchain.

Very cool, I've been waiting for something like this. btw if you have any trouble with ssl you could consider letsencrypt

So its not possible to remove a message?

It's not possible to remove a message embedded within the Bitcoin Blockchain. Locked Post assigns a sequential number to the beginning of every embedded message ("L1,Message" - sequence number "1" for example) - this acts as a easy way to verify that the data has not been modified or removed (by allowing anyone to check the sequence hasn't broken and that the web-site content matches what is stored in the Blockchain [The web-site provides links to various services that allow you to view Bitcoin transactions and therefore the embedded data within.]). You can see every message ever posted here: https://bitaps.com/1K69sEhUwNgiva3xzPnToxS89dzydU7nPm I will also eventually release code to easily verify the web-site.

http://pastebin.com/Ng7AFm3T/ - https://lockedpost.com/validate/PHP-Validation-Code/

Cool