Laboratories, abattoirs, furriers, hunters and intensive farming units in Europe and North America have been attacked. The Association of American Medical Colleges had by 1991 recorded over 4,000 cases of intimidation by animal rights activists. Considerable damage may be caused to research facilities using animals. Researchers themselves have been subject to bomb threats and injuries have been caused by letter bombs. In 1994, it was reported that over £5 million worth of damage had been caused for that year in the UK. An average of about 18 incidents a week included the use of 29 incendiary devices.