Freemasonry is a secret society.
All secret societies are satanic.
Freemasonry is the most well known secret society.
Freemasonry itself is a satanic organization, even if some of the Freemasons seem otherwise like "good guys."
Here is an overview of Freemasonry:
FreeMasonry isn't particularly secret either, you can find more about it online than you could by joining ffs.
Are you a Freemason?
I've made no secret of it, pun intended :)