Details have emerged of foreign agents hacking classified information from the mobile phones and laptops of two New Zealand trade negotiators travelling overseas.
A heavily redacted summary of the incident has been published on a government website.
The location of the incident was not disclosed, nor was the foreign power involved or the timing of the hack.
A summary said the two negotiators deleted information they considered sensitive from the devices before leaving New Zealand.
However, foreign intelligence officers accessed their hotel room and installed malware that logged activity even after the pair had returned to New Zealand.
The intruders also cloned the laptops' hard drives, and recovered the deleted documents as well as other sensitive material.
National Cyber Policy Office director Paul Ash would not discuss the specific case but said this was a rising problem.
"We have seen a steady rise in reports of cyber security problems or incidents in the last few years, we expect that will continue."
He said 316 had been recorded in the year to April, a 66 percent rise on the year before.