The breach saw the government's internal cloud-based directory of all territory public servants' government contact details exposed to hackers, in the first successful attack on a territory government website since 2012.

It comes at a time of increasingly sophisticated and numerous cyber attacks globally, including on Australia's Federal Parliament and government websites and, it was revealed on Monday, the country's largest political parties.

While the breach did not see ACT ratepayers' information exposed, the hackers did access the private home addresses of 14 public servants and personal email addresses of three public servants - information the group then tried to sell online.

The attack on November 23 last year was only identified after the Australian Cyber Security Centre identified a third party trying to sell the government's internal directory database to online buyers four days later.

After the territory government was told of the breach, it took a further 36 hours working with the ACSC and the federal police to close the vulnerability. The government would not identify the specific vulnerability, citing "ongoing security considerations".

A government spokeswoman said the hack involved a password spray attack, where a third party creates a program to spray accounts with potential passwords to gain access, and the November attack saw a "standard user account" compromised.

"This account access enabled the attacker to unlawfully gain a copy of the ACT Government Directory that included employee contact information including employee work address, email address, desk phone number and mobile phone number," she said.

"At no stage was any privileged or administrative access gained to the network citizen data held by the ACT government."

But she said personal information of some staff was accessed in the attack, including home personal email addresses and personal phone numbers - details public servants put in the directory themselves - and all those affected had been contacted.

The spokeswoman said that since the attack the government had worked on a plan to improve its cyber security and planned breach communications, and security had been increased with more use of multi-factor authentication, better password security and proactive monitoring.

She said the government was regularly the subject of such attacks, but there had been no other successful breach since an attack in 2012 on the justice directorate's website - which turned out to be a case of hackers mistaking the territory government's website for the Commonwealth justice department.

The government has also lodged a formal complaint with the federal police about the attack.