UPDATED  2.13PM: The SIS, New Zealand's internal security agency, played a part in blocking a man with terrorism-related convictions from entering the country, it has been revealed. 

The agency has published details about an incident in 2015 where it identified a person on a no-fly list as attempting to travel here.

The SIS raised the matter with Immigration officials who then discovered the person concerned had served a prison sentence for terrorism related charges.

It resulted in the person, who remains unidentified, as being blocked from boarding a flight to New Zealand.

The revelation comes with the SIS restating that it will be doing more work looking into the threat posed by the Islamic State and its ability to attract followers to its cause here in New Zealand.

The intelligence agency's annual report says the current anti-terror environment here continues to be dominated by the influence of the Islamic State.

It warns the group's propaganda output and pervasive social media presence is recruiting people to its cause here.

The SIS says it had between 30 to 40 people on its counter-terrorism risk register last year - people it describes as determined to represent an actual or potential threat to the country.

And it appears to be an area the SIS intends focusing on - the agency says it's to make further investments over the next 12 to 24 months in investigating violent extremism.

Meanwhile, the other chief spy agency is set to overhaul its computer systems.

The Government Communications Security Bureau (GCSB) has identified a need to extend and renew its IT infrastructure in its latest annual report.

The agency cited a rapidly changing technology landscape as having a disproportionate effect on its organisation, and also says there's a heavy demand on its IT infrastructure.

Specific costs for the project aren't revealed in the report, however it's set to come out of a $178 million funding package announced for the intelligence services in last year's Budget.