Weird "Virus Control" looks fake...?

randomly without my consent my computer started downloading a program and i later found out it was a virus control program that looks very fake and unofficial. after it downloaded the program said "free run of programs" on a pop-up and (foolishly) i said ok so it has been randomly scanning my computer and saying things that it hasn't before. now for the worst part, random websites keep popping up all of which involve gay porn, help me please, and i don't want any unofficial answers only if you no for sure how the heck to get rid of this. and if you needed to know it is an iMac