cat randomly urinating out of the litter box

One of my cats randomly pee-ed on the living room rug. They have used their litter boxes (which are cleaned daily) without problems since they were kittens. It happened while we were away at work. They are about 1 year old now. Any idea on why this would have happened? Thank you.

What did you clean the spot with? I agree, a vet visit is in order. Is your work schedule a new one?