I think is themida , or at least the virustotal.com it says like this but i am not shure.
From what i've been studying this L2FIX anticheat Engine it has an Server Side too that do some sort of autentification.
I am pretty shure is exencive piece of software considering ,until now is the best software for l2j on the market and is the only Auth that can BAN hardware equipent and not the IP (wich can be dynamic easily).
The thing that made me say WOW ... was when L2FIX detected HideToolz. That was the final drop that filled my mind and made me say : damn if this software gets around l2j servers i will never be able to have funn with PacketInjection.
But i also think there is no such thing as unbreakable protection. The only problem is to be patient enough to study how is done.
... i am pretty shure DragonHunter can break it.
PS: Tip : Search google with l2fix