Method #1

Add the following configuration to your web.config:

<system.web>
    <httpCookies httpOnlyCookies="true"  />
</system.web>

Method #2

In the code, use the System.Web.HttpCookie.HttpOnly property:

// Create an HttpOnly cookie.
HttpCookie theHttpOnlyCookie = new HttpCookie("LastVisit", DateTime.Now.ToString());
// Setting the HttpOnly value to true, makes
// this cookie accessible only to ASP.NET.
theHttpOnlyCookie.HttpOnly = true;
theHttpOnlyCookie.Name = "TheHttpOnlyCookie";
Response.AppendCookie(theHttpOnlyCookie);
// Show the name of the HttpOnly cookie.
Response.Write(theHttpOnlyCookie.Name);

References

http://msdn.microsoft.com/en-us/library/ms533046.aspx

Method

Add the following codes into the page, in order to prevent the page being cached:

Response.AppendHeader("Cache-Control", "no-cache, no-store, must-revalidate");
Response.AppendHeader("Pragma", "no-cache"); 
Response.AppendHeader("Expires", "0");

Reference

http://support.microsoft.com/kb/234067
http://wiki.asp.net/page.aspx/1487/prevent-browser-caching-of-web-pages-…
http://msdn.microsoft.com/en-us/library/ms178606(v=vs.100).aspx
http://support.microsoft.com/kb/q222064

Method #1 in web.config 

Add the following codes in web.config (In this example it is the timeout set for 15 minutes.

 <system.web>
    <sessionState timeout="15">
    </sessionState>
 </system.web>

Method #2 in Global.asax

Add the following lines to  Session_Start event of Global.asax

void Session_Start(object sender, EventArgs e)
{
   Session.Timeout = 15;
}

References

http://msdn.microsoft.com/en-us/library/ms525473(v=VS.90).aspx