The SIS broke into the Indian High Commission for MI6 and the Iranian embassy for the CIA in the late 1980s and early 1990s to photograph code books, plant bugs and steal communications.
The operations included at least two raids on the Indian High Commission in Wellington in 1989 and 1991 to photograph thousands of pages from the commission's code books - used to encrypt communications.
The covert attack on the Iranian embassy in Wellington was to bug the embassy and intercept communications from a Telex machine, in a mission driven by the CIA.
Sir Geoffrey Palmer and Jim Bolger, who were the two Prime Ministers for most of that period, say they were never told.
Investigative Journalist Guyon Espiner reports.