More than 50 members of the far-right British National Party in central Lancashire have had their personal details posted on the Internet.
An accountant, retired teacher, plasterer and three ex-servicemen were among those whose details were included in a leaked document.
Names, home addresses, telephone numbers and e-mail contact details were included on the entire membership list of more than 12,000 supporters.
The leak is a huge embarrassment to the party and a major breach of data protection.
Fourteen of the 56 central Lancashire members were described as being activists for the party.
Two couples appear to be listed and a family of three, the youngest of whom was 17 when he joined the party.
The party offers family membership of £40 a year.
The BNP has said its members could be vulnerable to violent attack as a result of the list's publication.
Some of those exposed will fear they could now be at risk of dismissal from work or disciplinary action.
BNP leader Nick Griffin claimed that he knew the identity of the person who published the list, describing him as a 'hard-liner' senior employee who left the party last year.
He said: "He didn't like the direction the party was going and broke away, taking the list with him."
The former serviceman was described on the list as an activist but said he was more of a "card carrying member".
It is thought the list may include lapsed members of the party and the names and addresses of people who have expressed an interest in joining the party but have not signed up.

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