Apostasy is forbidden in Islam. All apostates, those who chose apostasy, are the same as the unbelievers and all of them are vulnerable to the next Muslim bombing. Most Muslim scholars and jurists agree that the punishment for apostasy is death. Countries such as Iran and Saudi Arabia institute the death penalty for those who have left Islam i.e. apostates. The origin of this arbitrary and violent law is credited to Muhammad's fear of losing control over his followers. If they were to fear apostasy at the hands of death they would not question is totalitarian and irrational will.

Jewish people would call it apostasy.

Your question is unclear. Approximately 97% of the population are Muslims. Proselytising by other religions is prohibited. Apostasy (changing from Islam to any other religion) is punishable by death

No, it was religious fanaticism. Apostasy means going away from the "true religion" - that is, from whatever somebody believes to be the "true religion". Thus, apostasy might be changing from Christianity to Islam, or the other way around (depending on whom you ask). The 9/11 attacks had nothing to do with this.

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Some form of apostasy has been taking place since Cain rebelled against God, so any act that is contrary to the teachings of the true religion can be called a apostasy. The 9.11 cannot be called a true apostasy, though some would argue that it was as it was as it involved violence against ones fellow man. I suggest it may be called a rebellion against authority.