First four episodes of Game Of Thrones Season 5 leaked online week's before their official airing dates, and if you torrented these HBO is tracking down the downloaders and sending warnings to them.

Though no serious legal action is being taken as of now, HBO is sending thousands of emails instructing ISP's to relay the alerts to the account holder associated with the infringing IP-address. It is also worth nothing that since HBO doesn’t know the identity of the alleged pirates, they can't take any legal action directly as per the DMCA laws.