Prevent Browser Back Option

Use this following code to prevent the web browsers Back button options.

<script type="text/javascript">
        function preventBack() { window.history.forward(); }
        setTimeout("preventBack()", 0);
        window.onunload = function () { null };
</script> 

This will forward to the last history page.

JavaScript alert from UpdatePanel in ASPX (C#)

public void ClientMsg(string MsgTxt)
    {
        ScriptManager.RegisterClientScriptBlock(
        this.Page, 
        this.Page.GetType(), 
        "clientScript", 
        "alert('" + MsgTxt + "')", 
        true);
    }