These "look-alikes" have a common root in Latin (vertere,"to turn") but quite different meanings in English. Advert means "to refer," "to turn attention to," "to comment about": "He adverted to a topic mentioned earlier by another speaker." Avert means "to turn away or turn aside," "to prevent," "to ward off": "She averted her eyes from the injured man." "The driver braked hard to avert an accident."
Dictionary of problem words and expressions. Harry Shaw. 1975.