Reverse IP Lookup - blocked - How?

I just was looking at one of my sites via whois.sc and did an Reverse IP Lookup.
It listed the other domains on my server.

I did the same one another domain/IP and get ..

The search for 123.123.123.123 has been blocked.

I liked that ... How can that be achieved - are there any negative aspects?

 

 

 

 

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