Some other sites download stuff from ofpec (and elsewhere) and post it on their own site without permission. Providing they are not passing it off as somebody else's work, I suggest you just feel flattered that they thought it was worth the trouble.
If you care, or if they have done something you don't like, ask them nicely to take it down. They should have asked your permission first, no question about that. It's your mission and its up to you which sites have it.