Now, a wide-ranging review of New Zealand's SIS and GCSB has recommended a law change that would give the agencies access on a case-by-case basis to national student numbers.
Collected by the Ministry of Education since 2003, the identification numbers are assigned to every early childhood, school and tertiary student.
They are attached to information such as roll returns, and record of enrolment, to give an accurate picture of attendance and teaching.
The Government-ordered intelligence and security review, released this week, was completed by former Labour deputy prime minister Sir Michael Cullen and lawyer Dame Patsy Reddy after they were given high-level access to the workings of the agencies.
Asked why the agencies would need access to the student numbers, Sir Michael said the reason was primarily to do with international students.
"You will probably understand that we can't be sure that the large number of overseas students in New Zealand don't include some people who have other functions in life, apart from study."
There are about 54,000 international students at tertiary level in New Zealand.
In 2014, Fairfax reported that Chinese intelligence officials had confirmed that they were building informant networks to monitor Australia's ethnic Chinese community and temporary students from mainland China.
Much of the spying was reported as taking place at universities including Melbourne University and Sydney University, and the Australian Security Intelligence Organisation was said to have built new counter-intelligence capabilities as a result.
Hager said the SIS had long been interested in activity at universities -- from concern about Communism, to more recent interest in countering any attempts by foreign students -- particularly from Iran -- at acquiring knowledge that could be used to make a weapon of mass destruction.
"Our intelligence agencies tend to follow a succession of threat fads. We were concerned about al-Qaeda, and then we were concerned about Iraqis in New Zealand, heaven help us, around the time of the invasion of Iraq. And then we got locked into a period when we were concerned about Iranians in New Zealand, when the United States was talking about the threat of Iran.
"What it actually shows us is what intelligence agencies do that don't have real threats. Because if there were serious threats here, they wouldn't be messing around on the margins like this."
The intelligence and security report, containing 107 recommendations, will now be considered by the Government. No decisions have been made on any proposals. National hopes to get support from Labour for resulting legislation that could be introduced as early as July.
The report recommends a new single piece of legislation to govern both the activities of the SIS and GCSB, that would contain a beefed-up authorisation process, designed to safeguard privacy.
It also recommends an end to the current restriction on the GCSB intercepting New Zealanders' private communications. The distinction between the two agencies was now more about that technological capability, rather than any foreign or domestic mandate, the reviewers argued.
Hager said, without knowing how exactly any legislation will be worded, he suspected the move to free-up the GCSB to monitor New Zealanders was to clear away any barriers to the collection of Kiwis' metadata: "I think that is the main gift that [the reviewers] have given to the intelligence agencies".
The review was disgracefully compliant to the wishes of the intelligence agencies, he said.