钩子的本质是一段用以处理 系统消息的程序，通过系统调用，将其挂入系统。钩子的种类有很多，每种钩子可以截获并处理相应的消息，每当特定的消息发出，在到达目的窗口之前，钩子程序 先行截获该消息、得到对此消息的控制权。此时在钩子函数中就可以对截获的消息进行加工处理，甚至可以强制结束消息的传递。 而键盘钩子，只是为了截获键盘消息的。全局钩子可以捕获在Windows平台下任意窗口上的键盘操作-Hook is the essence of a message processing system to process calls through the system, be linked into the system. There are many types of hooks, each hook can intercept and process the corresponding message, whenever a particular message sent, prior to reaching the objective of the window, hook first intercepted the message, get control of this information. At this point in the hook function can intercept the messages on the processing, or even force the end of the message delivery. The keyboard hook, only to intercept keyboard messages. Global hooks to capture any window in the Windows platform on the keyboard