The email accounts of many ACT school students were inundated with large numbers of spam emails, including inappropriate material, on Friday.
An ACT government spokeswoman said the Education Directorate had investigated the incident and determined no external body had hacked its system or exported data.
"Students gained access to system email distribution lists and inappropriately used these to send emails to their peers," the spokeswoman said.
"This activity took place within the Education network and there has been no external security breach."
The spokeswoman confirmed the emails had included inappropriate material.
There were reports of links to pornographic websites and Instagram accounts being sent around and the solicitation of naked images.
It is unclear how many people had been affected, although it is understood to be many.
The spokeswoman said the full extent of the issue was being investigated by the Education Directorate and it was not yet known how many students had received the emails.
"The Education Directorate has responded by blocking access to the Google platform for all students," she said.
"Access will resume once the incident has been thoroughly investigated and appropriate controls put in place. Schools, parents and students are being advised if they received the email they should not forward it on and delete any copies they may have.
"The directorate will work over the weekend to review the material that was distributed, and will be following up as appropriate."
ACT Policing were notified of the incident and the directorate sent information to ACT public school families.
Education minister Yvette Berry requested a security review prior to the reactivation of the system over the weekend.
Some of the emails appeared to be long scripts of texts written in random characters.
Some school students appeared to have responded to the emails, which created a further chain of emails, and then others still sent more emails demanding the spamming stopped.
The spokeswoman said all high school and college students in the ACT have school email addresses, along with primary school students but predominantly from grade five and six.