I have a web service that I call via ajax that requires the user to be logged in. in each method I want to check if the user is logged in and send a 403 code if they are not, however when I call a Response.End() I get the error "Thread was being aborted". What should I call instead?

[WebMethod(true)]
public string MyMethod()
{
    if(!userIsLoggedIn)
    {
            HttpContext.Current.Response.StatusCode = 403;
            HttpContext.Current.Response.End();
    }
    /* Do stuff that should not execute unless the user is logged in... */
    ...
}