WHY DO MY CATS CHEW CORDS ALL OF A SUDDEN!?!?!?!?!?

also can other cats be a bad influence? can carma be playing a role in this? my friends house was getting fumigated so her cat Elfie was staying with me. that's when chewed up and severed cords first affected our lives. I made a comment like if my cat did that... or my cats would never do that.... then we noticed little nibbles in things and over the last few months its grown into an all out obsession and severed cords cover my house rendering our expensive electronics useless and putting us at risk for fire. I need help. I'm ready to crate the cats at night and when we are not at home. that's no life for kitties...but if we have no other option...