XCeptor
<script src="/tester.js"></script>
<script src="/xceptor.js"></script>
<script>
var xhr = new XMLHttpRequest();
xhr.open('GET', '?');
xhr.responseType = 'arraybuffer';
xhr.addEventListener('load', function() {
  var bytes = [].slice.call(new Uint8Array(xhr.response), 0, 7);
  Tester.feedback(String.fromCharCode.apply(String, bytes) === 'XCeptor');
});
xhr.send();
</script>