There are hundreds, possibly thousands of Palestinians working covertly for the Israeli intelligence services.
Without them it has been argued Israel's occupation of the West Bank would be far more difficult to sustain.
There would also probably be many more suicide bombings in Israel every year.
The collaborators in the occupied territories are absolutely vital sources of information for Shin Bet, Israel's internal security agency. And if they are caught they risk being killed.
Their actions are regarded by most Palestinians as the ultimate in treachery.
So why do they do it? For the money? For the thrill? For ideological reasons?
For Crossing Continents, Richard Miron gains the rare co-operation of Shin Bet and a unique insight into the way it handles the informants who work with it.
He speaks to collaborators who have been resettled in Israel and tries to discover their motivation, how they were recruited, what kind of information they provide to the Israelis, and what problems they now face - hated by Israeli Arabs, distrusted by Israeli Jews and unable to return home.
Crossing Continents was broadcast on Thursday, 14 December 2006, at 1102 GMT and repeated on Monday, 18 December 2006, at 2030 GMT.
Presenter: Richard Miron
Producer: David Edmonds
Editor: Sue Ellis