防止程序各类漏洞入侵的最后一道防线，将checkip.asp包含在后台文件中，这样别人就算拿到了正确的用户名密码也进不去后台-Prevent the program all kinds of exploits last line of defense, will checkip.asp included in the spool file, so even if someone else got the correct username and password can also get in