user69241: According to this post, I can store arbitrary data in the blockchain (as the news about "child pornography in the blockchain" tell).
Now I want to store "Hello World" in the blockchain.
Is there a newer website/service that supports me putting data into the blockchain?
And what's the difference between a transaction in the blockchain and such a "message"?
Is the structure different? Why could those researchers even find out that it's inappropriate content instead of a default transaction?

user12983: Have a look to these data sources:

https://bitcointalk.org/index.php?topic=1023190
https://github.com/petertodd/python-bitcoinlib/blob/master/examples/publish-text.py

And of course the "modern" (and cheapest) way is storing arbitrary data in segwit part of transactions. I do not know is there ready tool for it, but it is not very difficult to write it.

Is there a newer website/service that supports me putting data into the blockchain? 

https://cryptograffiti.info/ (based on bitcoin cash blockchain)

69241: <p>According to <a href="https://bitcoin.stackexchange.com/questions/1881/how-can-a-non-miner-store-data-in-the-block">this post</a>, I can store arbitrary data in the blockchain (as the news about "child pornography in the blockchain" tell).
Now I want to store "Hello World" in the blockchain.</p>

<p>Is there a newer website/service that supports me putting data into the blockchain?
And what's the difference between a transaction in the blockchain and such a "message"?
Is the structure different? Why could those researchers even find out that it's inappropriate content instead of a default transaction?</p>
 12983: <p>Have a look to these data sources:</p>

<ul>
<li><a href="https://bitcointalk.org/index.php?topic=1023190" rel="nofollow noreferrer">https://bitcointalk.org/index.php?topic=1023190</a></li>
<li><a href="https://github.com/petertodd/python-bitcoinlib/blob/master/examples/publish-text.py" rel="nofollow noreferrer">https://github.com/petertodd/python-bitcoinlib/blob/master/examples/publish-text.py</a></li>
</ul>

<p>And of course the "modern" (and cheapest) way is storing arbitrary data in <strong>segwit part</strong> of transactions. I do not know is there ready tool for it, but it is not very difficult to write it.</p>

<blockquote>
  <p>Is there a newer website/service that supports me putting data into the blockchain? </p>
</blockquote>

<p><a href="https://cryptograffiti.info/" rel="nofollow noreferrer">https://cryptograffiti.info/</a> (based on bitcoin cash blockchain)</p>
