About login session
===

I'm doing my project about developing a website.I'm new to ASP.net and now I have a problem about login session that when a user logged on, everyone who is surfing the web at the same time is also logged as that user no matter they login or not. The session only end when someone click on Logout button and everyone is logged out. Please help me. Every help would be appreciated. 
 Here is my code, I code these thing in my Master page:


     protected void Page_Load(object sender, EventArgs e)
    
        {
    
            string equip = "Equipment.aspx";
            string url = HttpContext.Current.Request.Url.AbsoluteUri;
            if (url.IndexOf(equip) != -1) { Calendar2.Visible = false; Image1.Visible = false; }
            equip = "Bookings.aspx";
            if (url.IndexOf(equip) != -1) { Calendar2.Visible = false; Image1.Visible = false; }
            equip = "Rooms.aspx";
            if (url.IndexOf(equip) != -1) { Calendar2.Visible = false; Image1.Visible = false; }
            equip = "Users.aspx";
            if (url.IndexOf(equip) != -1) { Calendar2.Visible = false; Image1.Visible = false; }
            
            if (!Page.IsPostBack)
            {
                if (user != "" && user != null)
                {
                    loginStatus = true;
                    redirectpage = false;
                 
                }
                else
                {
                  
                    redirectpage = false;
                    loginStatus = false;
                    user = "";
                    authority = 0;
                }
                
            }
            else
            {
                
                if (user == "" || user==null)
                {
    
                    if (cal != null)
                    {
                        
                    }
                    loginStatus = false;
                    authority = 0;
                }
                else
                {
                    if (cal != null)
                    {
                        
                    }
                    loginStatus = true;
                }
            }
        }
    
     /// <summary>
     /// Responds to a login request, validating details against the database and
     /// loading the user into the session if successful.
     /// </summary>
     /// <param name="sender">The sending object.</param>
     /// <param name="e">The event arguments.</param>
    
     protected void Login_Authenticate(object sender, AuthenticateEventArgs e)
     {
    
     SqlConnection oConn =
     new SqlConnection();
     oConn.ConnectionString = @"Data Source=STAVROS\SQLEXPRESS;User ID=sa;Password=123abc;Initial Catalog=webdev";
    
     sSQL = "select * from tbl_user where username = '" + Login.UserName + "'AND password = '" + Login.Password + "' ";
     SqlCommand oComm1 = new SqlCommand(sSQL, oConn);
    
     try
     {
    
     oConn.Open();
     SqlDataReader i = oComm1.ExecuteReader();
     if (i.HasRows)
     {
     while (i.Read())
     {
     user = i.GetString(0);
     authority = i.GetInt16(7);
    
     loginStatus = true;
     string url = HttpContext.Current.Request.Url.Absolute…
     string p = "Home.aspx";
     if (url.IndexOf(p) != -1) { Response.Redirect("Home.aspx"); }
     Helper.CreateUserSession(Session, user);
     }
    
     }
     else
     {
     loginStatus = false;
     Login.FailureText = "Invalid username or password.";
     }
    
    
     i.Close();
     }
     catch (Exception ex)
     {
     Response.Redirect("room-book.aspx");
    
     }
    
     }
    
     /// <summary>
     /// Logs the user out (kills the session)
     /// </summary>
     /// <param name="sender">The sender</param>
     /// <param name="e">The event arguments</param>
    
     protected void btnLogout_Click(object sender, EventArgs e)
     {
    
     loginStatus = false;
     user = "";
     authority = 0;
     Response.Redirect("Home.aspx");
     }