Israel is not America’s closest ally, at least when it comes to whom Washington trusts with the most sensitive national security information. That distinction belongs to a group of nations known informally as the “Five Eyes.” Under that umbrella, the United States, Britain, Australia, Canada and New Zealand agree to share intelligence and not to spy on one another. Often, U.S. intelligence officers work directly alongside counterparts from these countries to handle highly classified information not shared with anyone else.

Israel is part of by a second-tier relationship known by another informal name, “Friends on Friends.” It comes from the phrase “Friends don’t spy on friends,” and the arrangement dates back decades. But Israel’s foreign intelligence service, the Mossad, and its FBI equivalent, the Shin Bet, both considered among the best in the world, have been suspected of recruiting U.S. officials and trying to steal American secrets…

During the Bush administration, the CIA ranked some of the world’s intelligence agencies in order of their willingness to help in the U.S.-led fight against terrorism. One former U.S. intelligence official who saw the completed list said Israel, which hadn’t been directly targeted in attacks by al-Qaida, fell below Libya, which recently had agreed to abandon its nuclear weapons program.