The pair of Bulgarian journalists who run anonymous leaking site BalkanLeaks say they have received threats after releasing secret documents exposing Bulgarian Prime Minister Boyko Borisov's alleged mafia past.

A leaked document recently released by BalkanLeaks' news website Bivol.bg revealed that current Prime Minister, Boyko Borisov, was recruited in the past as a secret agent of the Central Services for Combatting Organized Crime, CSBOP.

Borisov was allegedly recruited as informant over his close ties with the mafia. A 1997 file, which refers to Borisov under the codename "Buddha," notes his "criminal orientation" and suggests "clarifying connections of the subject with people and businesses linked to criminal activities."

The journalists behind BalkanLeaks and Bivol.bg have now told Forbes contributor Andy Greenberg that they have accompanied their latest leak with a new defensive measure - an encrypted insurance file with a key that will only be released if BalkanLeaks' staff are arrested or feel that their lives are threatened.

"In response to threats made against its journalists, Bivol is now releasing this insurance file. The key will leak automatically if something happens to our staff," reads a note posted to BalkanLeaks' website. The note asks supporters to download the file and share it via bittorrent in order to make it more difficult to censor.

The release follows a series of anonymous threats posted to online forums and a cyberattack against the website that took it offline for 12 hours earlier this month.

"We are up against a mafia-state nexus," BalkanLeaks co-founder Atanas Tchobanov has told Andy Greenberg. "We need insurance."

Andy Greenberg's article can be read HERE.