What is this growing on my Acropora?

[ThRoewer]

What is this on my coral:

I noticed this a while ago, first on a favia and then on this acropora. It looks like some form of hydroid polyp. It seems to penetrate the coral tissue and attach to the skeleton.
So far I can't see that it is doing any direct harm but now I noticed this or something similar also on other acroporas.

What is it and how to get rid of it?

 

[smtank]

Looks like hydroids to me as well.

 

[Eastone]

I see these too, they don't seem to cause issues but my new dwarf angel has been picking at them