Pornographic images were found on publicly funded computers used under the federal government's Northern Territory intervention programs in indigenous communities.
The Department of Families, Housing, Community Services and Indigenous Affairs (FaHCSIA) has conducted regular audits of computer files in conjunction with the Australian Crime Commission (ACC).
Letters from the ACC to the department, marked "highly protected", and released under freedom of information laws, say pornographic images were stored on NT publicly funded computers and that pornography websites had been accessed.
A December 2010 audit found "39 suspected images" on computers at eight organisations, the letters.
The June 2010 audit found "106 suspected pornographic images or web pages accessed at 15 organisations".
The letters said the December 2009 audit found "85 suspected pornographic images or web pages accessed from seven organisations" while the June 2009 audit found eight organisations had a total of "145 suspected images or web pages".
"Comparative analysis of the December 2008 and June 2009 audits have shown a significant drop in detected images and web pages from 1229 to 145," a document says.
The December 2008 audit found "illicit activity" across 13 organisations' computers.
In each letter, the ACC urges the department to try to have its correspondence about the audits exempted in the event of freedom of information requests.
The NT intervention began in 2007 under the Howard government and was continued under Labor.
Last year, it was extended for a decade and rebranded Stronger Futures.
Comment is being sought from Indigenous Affairs Minister Jenny Macklin.