Parasite removed from my brain coral....

I just acquired an open brain, (my first), a few weeks ago.
It was doing great, but then I noticed this wart-like hole that seemed to be
getting tissue damage around it.
I watched it during a spot feeding and saw little legs coming from the hole.
I pulled this out:

http://www.highwaymp3.com/ebay/parasite1.jpg

It looks like a hermit crab out of its shell. 1/4" long.
The area around the hole was becoming necrotic and that is why I noticed it.
I have read a lot of books, but never seen this.
It left a gaping hole in the coral and a deep conical hole in the skeleton,
right on the edge between two of the sharp skeleton lobes. It appears to
have bored in.

Q1: What the hell is it?
Q2: Did I do the right thing by removing it?
Q3: How can I best comfort the coral while it heals?
Q4: Was it already there, or do you think it was in my tank and moved in
after I placed it...

CW
(shocked and a little sick to my gizzard)