What kind of worm? If it is long and thin like a fettucini noodle with segments, it's a tapeworm and needs to be taken care of ASAP. Either way, take your cat to the vet and get it wormed as soon as you can. Those tapeworms stick to their intestines and just get longer and longer and longer and will eventually lead to your cat becoming emaciated because the worm will absorb all of the nutrients in the cat food before the cat itself can get any.