The son of a leading Hamas figure, who famously converted to Christianity, served for over a decade as the Shin Bet security service's most valuable source in the militant organization's leadership, Haaretz has learned. Mosab Hassan Yousef is the son of Sheikh Hassan Yousef, a Hamas founder and one of its leaders in the West Bank. The intelligence he supplied Israel led to the exposure of a number of terrorist cells, and to the prevention of dozens of suicide bombings and assassination attempts on Israeli figures. The exclusive story will appear in this Friday's Haaretz Magazine, and Yousef's memoir, "Son...