Floo powder is not safe at the moment, the Network is being watched. You will be taking a Portkey.
-- Albus Dumbledore
After Harry’s vision of Arthur Weasley being attacked by a giant snake, Dumbledore sends them directly from his office to Grimmauld Place by means of a Portkey. He allows them to get away from Hogwarts before Umbridge is alerted that they are out of bed.