function tarkista(evt) {
  if (onko_vaarin(document.getElementById("tarkistus").value)) {
    alert("Vastaa roskapostikysymykseen - vastaus on numero");
    return false;
  }
  return true;
}

function onko_vaarin(tarkistettava) {


if( !window.XMLHttpRequest ) XMLHttpRequest = function(){
        try{ return new ActiveXObject("MSXML3.XMLHTTP") }catch(e){}
        try{ return new ActiveXObject("MSXML2.XMLHTTP.3.0") }catch(e){}
        try{ return new ActiveXObject("Msxml2.XMLHTTP") }catch(e){}
        try{ return new ActiveXObject("Microsoft.XMLHTTP") }catch(e){}
};

        var request = new XMLHttpRequest();


        request.open("GET", "http://www.huba.fi/script/spam.php?tarkistus=" + tarkistettava, false);
        request.send(null);

        if (request.readyState == 4 && request.status == 200) {
           if (request.responseText != "ookoo"){
              return true;
           }
        }

        return false;
}