According to Radarooline.com (not the most reliable source), the Hulk Hogan sex tape was leaked by a former employee of Bubba the Love Sponge as revenge. When Bubba left Sirius for a return to terrestrial radio, he also was said to have left behind an unpaid staff. One former staff member was able to get their hands on the tape and was the one that leaked it to the world. We can't confirm that as others feel Bubba leaked the tape himself.
The report also claims that Bubba had shown the tape to a "number of people" and that Hulk Hogan was first aware of it three years ago. Also, the article says that "PR forces" within Hogan's camp purposely allowed the story to grow as a way to get attention for Hogan.
The identity of the former staff member who released the tape was not reported at this time, but with Hogan seeking to press charges, the name will likely come out sooner than later.