How to stop ASP.NET bypass login using SQLSERVER 2005

SqlConnection conn = new SqlConnection();
conn.ConnectionString = System.Configuration.ConfigurationManager.ConnectionStrings["your connection string name"].ConnectionString;
conn.Open();
SqlCommand cmd = new SqlCommand("Select uname, pswd from table where uname = @id and pswd = @password ", conn);
cmd.Parameters.Add(new SqlParameter("@id", "id here"));
cmd.Parameters.Add(new SqlParameter("@password", "password here"));
SqlDataReader dr = cmd.ExecuteReader();
if(dr.Read())
{
     //Username and password found.User exists.
}
else
{
        //Username or password not found.Throw error message.
        Response.Write("<script type='text/javascript'>");
        Response.Write("alert('Invalid Credentials.');");            
        Response.Write("</script>");
}