How are servers found on the internet that have no name registration?

I don't know, if people have this problem. Recently I saw a video of a person talking about it in youtube, and I found myself related to it. It seems that when you set up a server on the internet you very rapidly you start getting ssh dictionary attacks, even though you have a dynamic ip assignment and no name registration. I've tried in the past to do a network lookup for my subnet internet provider to see if I can see other computers, but it seems that the network provider blocks those messages.

So I'm curious how are hostile users of the internet finding servers so fast?

If anyone can bring some light to this problem will be appreciated.

Regards