Virtue and Knowledge - Plato, Socrates

The questions that were pondered in Plato's Protagoras were; is virtue knowledge, and can virtue be taught. Protagoras' position was that virtue and knowledge are different things and that virtue can be taught. Socrates, on the other hand, held that virtue is knowledge, but that it can't be taught. Keep in mind that Protagoras and the other Sophists claimed to be teaching virtue.