The worst examples of corruption came from the Voldemort fiasco where he refused to acknowledge his return. He then set out on a mission to destroy their reputations using any means possible. He changed two laws. One in order to get Harry a trial so he could personally prosecute him, and the next was he changed a law so that he was allowed to put Dolores Umbridge as the Defense Against the Dark Arts in Hogwarts with room for a promotion by Fudge