Actually, it seems that it was actually honest hacking. Basically, the site does some fancy coding that's not too fancy for showing videos, and that coding is left in the computer's cookies. Someone took a look and found out that episode 3's code had the date of 18/4/2012, so doing a bit of hacking that person easily got to a part of the site where file names are asked for, with a program he generated directions that ended with 25/4/2012 in that day until the episode started playing for him/her, and well, less than a day later the leak fully happened.