Helaman 1

As a warning to us today, Mormon writes that their was a group that -

"...raised up in rebellion and sought to destroy the liberty of the people."  (Helaman 1:8)

And in doing so - 

"...they all entered into a covenant, yea, swearing by their everlasting Maker, that they would tell no man..."  (Helaman 1:11)

And thus - 

"...did mingle themselves among the people, in a manner that they all could not be found..."(Helaman 1:12)