Four animal rights activists were convicted Tuesday of blackmailing companies that supplied an animal testing laboratory.

A jury in Winchester, southern England, convicted Gerrah Selby, Daniel Wadham, Gavin Medd-Hall and Heather Nicholson of orchestrating a campaign against suppliers of Huntingdon Life Sciences between 2001 and 2007.

They will be sentenced on Jan. 19 along with three people who earlier pleaded guilty to conspiracy to blackmail.

One defendant, Trevor Holmes, was acquitted.

Huntingdon Life Sciences has been a long-standing target of animal rights extremists.

The four, members of Stop Huntingdon Animal Cruelty, used threats such as claiming that company managers were pedophiles, sending hoax bombs, dumping paint stripper on an executive's car and making threatening telephone calls.

Campaigners also mailed used sanitary towels to a company, claiming they were infected with the AIDS virus, and homes of company managers were daubed with slogans including "puppy killer" and "Bill the murderer."

The harassment would stop only when a company put out a "capitulation statement" to SHAC promising not to supply Huntingdon Life Sciences, which conducts animal testing for the pharmaceutical industry.

Targeted companies included GlaxoSmithKline, Astellas, F2 Chemicals and Biocair, prosecutors said.