In the short few days since the start of term, everyone had basically figured out Umbridge's personality: she was a hypocritical, self-righteous, unreasonable, and bossy old woman.
Not a single Prefect who had dealt with Umbridge liked her.
Nobody knew which Prefect had secretly leaked the contents of their conversation with Umbridge, but word was already spreading around the school that Umbridge wanted the Prefects to act as her spies to monitor the students of Hogwarts.
Chapter 933