They are using the SlowAES java script library to mark your browser with a encrypted AES string using an INDIVIDUAL secret/challenge for you, it is being stored in your browser. Can it be used to handle DDOS? No. DOS? Yes. But it is taking away all your anonymity, you are not 127.0.0.1 anymore, instead you are 127.0.0.1 plus your unique encrypted string. So it can also be used to track you.
If it is a legit case, it is actually a simple flood DOS attack 'cause it is the only kind of attack that Java Script can protect. Otherwise it is LE.
javascript is one word