For decades Palestinian propaganda has been urging Palestinians to unite and destroy Israel. This strategy has not worked well, and one of the major reasons is the corruption. If there is one constant complaint among Palestinians it’s the corruption they confront every day from other Palestinians, especially those who are supposed to be their leaders. They get much less of this bad behavior from the Israelis. The corruption is most pernicious within the Palestinian community and repeated efforts to deal with the problem have failed. While hated by Palestinians, the culture of corruption is a major asset for Israeli intelligence and counter-intelligence forces.
Hamas, for example, has always known about the Israeli informant network in Gaza and the difficulty in eliminating it or, more realistically, doing some damage to it. The key to Israeli success in dealing with Palestinian terrorists has always been informant networks within the Palestinian community. Many of these Palestinian informants are doing it for the money. Israelis pay for information, just like Palestinians must pay bribes to get anything done by their own bureaucracy in the Palestinian territories. Israelis also use other inducements (help with the bureaucracy, medical care, etc). If that fails, they use blackmail and threats. Palestinian terrorist organizations have been unsuccessful in their attempts to shut down the informant networks, and many innocent Palestinians have died simply because they were falsely accused of being informants. Worse for Palestinian terrorists, the informer network also exists inside Israeli prisons and many a Palestinian prisoner has found themselves facing another prosecution because of an inadvertent confession they made to a fellow “prisoner” (who turned out to be an Israeli Arab with a convincing cover story and believable accent).
In addition, the Israelis gain a lot of information via electronic intelligence work and UAVs that are constantly in the air over Gaza. Israel seeks to make the terrorists think that it's the gadgets, not informants, gathering the information. To the Israelis, inducing paranoia among the Palestinians is seen as a successful weapon. All this has helped keep the terrorists out of Israel for over a decade now, something no one thought was possible.
Israel also has hundreds of police and military operatives who can pass as Arabs. That's because the families of these Israelis came from Arab countries shortly after Israel was founded in 1947. These Israelis speak fluent Arabic (with a Palestinian accent), in addition to their Arab appearance. These agents dress as Palestinians and enter Palestinian areas to recruit and run Palestinian informants, at least in the West Bank. In Gaza, the Israelis use pro-Fatah (the rival group that runs the West Bank) Palestinians. At least a third of the Gaza population is still pro-Fatah, and continued Hamas pressure has not changed that.
Meanwhile, telecommunications hacking has become a major part of Israeli espionage over the last decade, which accounts for more "Israeli spies" being caught. Israel recruits people in Arab telecom companies, a lot of people. Some get caught. But Israel has been able to hack into cell phone systems and monitor the Internet in Arab countries. Information, for Israel, is a matter of survival.
Obtaining that information is much easier because of the culture of corruption often found in Arab communities. Mix this with the Israeli ability to put a lot of Israelis from Arab backgrounds out there and you have a constant problem that the Palestinians and Arabs in general have not been able to overcome.