Alan Thomas was so angry with ACC that he hatched a plan to park a van full of explosives and nails outside a branch office, set off the building's fire alarm and explode the bomb as staff gathered outside.

When police raided the 55-year-old beneficiary's North Shore home, they found bomb-making manuals on his home computer.

Thomas told the officers he had not read them.

After ACC learned of the threat, it employed extra guards at its offices and revamped security at a cost of more than $16,000.

Yesterday, Thomas was sentenced in the North Shore District Court to 10 months of home detention.

ACC sought reparation from the prisoner for the increased security costs, and Judge Lawrence Hinton ordered him to pay $5000 at $100 a month.

Thomas had earlier pleaded not guilty to threatening to kill or do grievous bodily harm to Accident Compensation Corporation staff.

An associate of Thomas told the hearing last year of discussions in May 2007 about bombing ACC.

The pair met through a website where ACC claimants discuss their cases in an online forum.

The witness told the court last year that he initially treated it as a "passing comment".

But the conversations continued and Thomas told the man of his plan to bomb ACC's Takapuna branch.

The witness said about 20 discussions took place before he told Thomas he wanted nothing more to do with him. He told another associate, who passed the information to ACC.

Judge Hinton found Thomas guilty.

"He toyed arrogantly with the lives and safety of those who were going about their day-to-day jobs in a public institution," the judge said at yesterday's sentencing.

Defence lawyer Nigel Cooke said Thomas never had the means to put the alleged plan into action. The police prosecutor agreed.

Mr Cooke said his client maintained his innocence, and had brain damage.

"Because of that, in my submission, this man is not a person in the know who you would describe as in the 100 per cent category."

Mr Cooke said his client did not own a van.

But Judge Hinton said the threat against ACC staff was especially sinister as it targeted people who would have thought they had fled to safety.

"The threat concerned a body of people representing an institution which Mr Thomas hates. The target of the threat was not the institution but the people of the institution.

"Some of these people in the institution he hates would never have had anything to do with him."

Thomas had a "deep-seated hostility to ACC".

Judge Hinton said the probation officer who visited Thomas was shown many ACC files "meticulously packed away in folders".

"It is clear Mr Thomas has a compulsive obsession with ACC which he seems evidently quite proud of."

According to the court file, Thomas was found guilty in 2000 of 22 fraud charges relating to ACC, and was sentenced to three years in prison.

The Herald reported that at the time Thomas was receiving ACC compensation, he wrote articles entitled "How to become a millionaire" and the "Money Machine" and was photographed introducing then Finance Minister Bill Birch to a seminar.

He received $238,000 in accident compensation over seven years while also earning from an immigration consultancy, publishing a Chinese newspaper and teaching English.

A police document in the latest case said Thomas had been battling ACC over an injury to his wrist for 15 years, and had been barred under trespass laws from all ACC offices in the country.