The militants, who included three women, targeted scores of victims over a six year period and attempted to force the closure of animal testing firm Huntington Life Sciences.
Hoax bombs and sanitary towels allegedly contaminated with HIV were sent to companies that did business with the Cambridgeshire based research laboratory in an attempt to create a "climate of fear".
One individual and his family were "persistently targeted" over nearly four years, with letters sent to his neighbours telling them that he was a paedophile, a threatening letter sent to him saying that someone would stab him with an HIV-infected needle, and the word "murderer" daubed on the entrance of his village railway station.
The managing director of another company received a letter in December 2006 that threatened: "We will attack your property, your family or you, whichever we see fit . . . The screams of the animals are in our heads. We will not fail them. You will pay for their agony."
The campaign was run with "military precision" across Europe by an organisation called Stop Huntington Animal Cruelty (Shac), who also operated under the banner of the Animal Liberation Front. The activists had links with extremists in the US and Europe allowing them to target HLS and its suppliers, both in the UK and abroad.
William Denison, managing director of a company with only very indirect links to HLS, said his family's life was turned into a "living hell" for six months when he was targeted. He said a hoax bomb was sent to his home and letters alleging that he was a paedophile were sent to up to 200 families in his village near Preston, Lancs.
Mr Denison said this had a massive impact on his family because his wife worked as a children's special needs assistant and he helped create floats for local children's events.
Fourteen slogans, including "Bill the murderer" and "Bill the ALF (Animal Liberation Front) are coming for you" were painted in red on a 500 yard stretch of road near his home.
A PA at another company had her house and car daubed with paint saying "puppy killer".
Two of Shac's founding members, Gregg Avery, 41, and his wife Natasha, 39, along with fellow activist Daniel Amos, 22, pleaded guilty earlier this year to conspiracy to blackmail.
Yesterday, following a three-month trial at Winchester Crown Court, Avery's former wife and fellow SHAC founder Heather Nicholson, 41, were found guilty of the same offence.
Three further conspirators, Daniel Wadham, 21, Gerrah Selby, 20 and Gavin Medd-Hall, 45 were also convicted. All will be sentenced next month.
Det Ch Insp Andy Robbins, of Kent Police, said: "This conspiracy to blackmail involved the systematic and relentless intimidation of individuals and their companies who the defendants suspected them to be involved with HLS."