如何绕过这个“在线学习防挂机”限制？？？

[aliwy]

一个在线学习网站，如果15分钟没有任何操作，就会自动退出。
从网站上看到这段“防挂机”代码如下，请教如何绕过这个限制！

var PageTimeCounter = 0; //初始化页面挂机时间倒计时
var ShutdownCounter = 0; //初始化提示窗口关闭倒计时
var PageTime = 900; //定义页面弹出关闭信息时间，单位秒
var ShutdownTime = 300; //定义关闭信息持续时间，单位秒
var MsgStatus = "hide"; //初始化弹出消息显示状态
var ShowPop; //显示弹出消息
var HidePop; //隐藏弹出消息
function ready() {
    var PopMessage = document.getElementById("PopMessage");

    $(document).mousemove(function () { ChangeToMaskLess(); if (MsgStatus == "hide") { PageTimeCounter = 0; ShutdownCounter = 0; }; });
    document.getElementById('PopMessage').style.height = '0px';
    setInterval('ChangeToMask()', 5000);
    setInterval('CheckPageTime();', 1000);
}

function ChangeToMask() {//启用遮罩层，To-Hack-iframe
    var MaskDivZindex = document.getElementById("MaskDiv");
    MaskDivZindex.style.zIndex = "0";
}

function ChangeToMaskLess() {//禁用遮罩层，To-Control-iframe
    var MaskDivZindex = document.getElementById("MaskDiv");
    MaskDivZindex.style.zIndex = -100;
}

function CheckPageTime() {
    if (PageTimeCounter < PageTime)
        PageTimeCounter++;
    else
        PageTimeCounter = PageTime;
    $('#show').text(PageTime - PageTimeCounter); //页面挂机时间倒计时
    $('#ShowShutdownCounter').text(ShutdownTime - ShutdownCounter); //关闭当前浏览器窗口倒计时，以秒显示
    $('#PageTime').text((PageTime / 60).toFixed(0)); //页面挂机时间设定值,以分钟显示
    if (PageTimeCounter >= PageTime) {
        Show_Notice();
    }
}

function ShutdownPage() {
    ShutdownCounter++;
    if (ShutdownCounter >= ShutdownTime) {
        Exit();
    }
}

function Exit() {//强制关闭当前浏览器窗口
    window.opener = null; window.open("", '_self', ""); window.close();
}

function Show_Notice() {
    var PopMessage = document.getElementById("PopMessage");
    var popH = parseInt(PopMessage.style.height); //将对象的高度转化为数字
    PopMessage.style.display = "block";
    ShowPop = setInterval("changeH('up')", 20);
    ShutdownPage();
}

function Close_Notice() {
    PageTimeCounter = 0;
    ShutdownCounter = 0;
    var PopMessage = document.getElementById("PopMessage");
    var popH = parseInt(PopMessage.style.height); //将对象的高度转化为数字
    PopMessage.style.display = "block";
    HidePop = setInterval("changeH('down')", 20);
}

function changeH(str) {//显示和隐藏退出提示框
    var PopMessage = document.getElementById("PopMessage");
    var popH = parseInt(PopMessage.style.height);
    if (str == "up") {
        if (popH <= 100) {
            PopMessage.style.height = (popH + 4).toString() + "px";
        }
        else {
            clearInterval(ShowPop);
            MsgStatus = "show";
        }
    }
    if (str == "down") {
        if (popH >= 4) {
            PopMessage.style.height = (popH - 4).toString() + "px";
        }
        else {
            clearInterval(HidePop);
            PopMessage.style.display = "none";
            MsgStatus = "hide";
        }
    }
}

$(document).ready(ready); //启动主程序