This is not the first time. In 2003, after Helen Clark's jumped up "Spy Scandal" there were four separate attacks in 6 Months.
This is most likely the work of the far right morons known as "Right Wing Resistance" or some such that were having conferences this labour weekend. They are so small in numbers and stupid that I seldom blog about them. Still dangerous, apparently. Unlikely to win too much respect with cowardly acts like this.