Cassandra's hand went into the air. "Defensive spells are what you use in a duel, to protect yourself. Something immediate, most times temporary." She smiled proudly, "While a security charm, is something you leave in place for the perpetrator to deal with when they show up. Not immediate, not used in a duel. Something more permanent, and set. The Fidelus charm, for instance, lasts until the secret keeper passes away."

Although Cassandra did not smile, she beamed at her professor and former Head of House.