A USB stick inserted in a carpark booth computer at Waikato Hospital has been blamed for bringing down the district health board's computer network in December last year.

About 3000 computers across the board's network were infected with the Conficker virus, forcing a complete computer shutdown.

Wilson Parking northern general manager Stephan Wuffli told the Waikato Times the source of the virus appeared to be from a USB stick that was used in a computer in a carpark booth. The booth was linked to the DHB computers.