Photos on the social networking website Facebook are meant to embarrass students - not their professors. But the cheeks of the president of the University of Pennsylvania, Amy Gutmann, have been a little red of late after a photo of her with a student dressed as a suicide bomber was posted on the site. The undergraduate, Saad Saadi, came to Gutmann's Hallowe'en party wearing camouflage trousers with fake dynamite strapped to his shirt. He was brandishing a fake gun and in some of the pictures appears to be reading the Koran. Dr Gutmann said that as she posed with Saadi she had been unaware of what the costume implied.