The Government Communications Security Bureau website was attacked by hackers earlier today.
A spokesman for the organisation said although the attack did not shut down the website, it slowed the website's gateway for about 30 minutes.
"... There is an indication there could have been some temporary degradation of service."
It is believed the website suffered a DDoS or distributed denial-of-service attack, where a website suffers a saturation of external communications requests to the point that it cannot respond to legitimate traffic in an attempt to cause the server to overload.
The attack did not affect GCSB operations in any way the spokesman said.
A Twitter page with the handle 'OpF*ckGCSB' tweeted "#TangoDown" and a screen shot showing the website down.
The Twitter user claimed links to the international 'hacktivist' group Anonymous.