Federal government departments are using increasingly powerful cyber-snooping equipment to monitor the social media lives of millions of Australians.

A dramatic public confrontation between the Immigration Department and a Sydney political activist over her Facebook page has resulted in accusations that mass-electronic surveillance is being used to keep tabs on political dissent.

Other large government departments including Centrelink, Defence and Social Services have done mass monitoring of social media activity.

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Centrelink's parent agency, the mammoth Department of Human Services, even has its own software, developed by the CSIRO and operated by a social media team of 10 public servants.

The Department of Immigration and Border Protection (DIBP) hires private sector contractors who can monitor more than half-a-billion ''pieces'' of social media each day on sites like Facebook, Twitter, YouTube, Pinterest, Flickr and blogs.

Several commercially available social media-tracking platforms, some of them in routine use by public service online media teams, can easily track the web activities of protest groups and their individual members.

Immigration experimented several years ago with powerful software called Radian6, which can provide surveillance across a range of social web platforms, but decided not to adopt the application for in-house use.

The department's key research contractor said the monitoring undertaken for Immigration was about ''taking the temperature of society'' and that no reputable research company would help government departments compile ''hit lists'' of political opponents.

But pro-asylum seeker campaigner Vanessa Powell said she was intimidated and threatened when the DIBP tweeted her about an ''offensive remark'' it said should be removed from her Facebook thread immediately or the government would ''consider our options further''.

''I felt quite intimidated and threatened as well because I didn't know what action they were referring to when they said 'we will consider our options further','' Ms Powell said.

When she identified the post in question - a comment using ''foul language'' a friend made about a photograph of a protest at a Sydney detention centre - she removed it.

''I was shocked that they were actively monitoring my account because it's just my personal page,'' Ms Powell said. ''They have no right to be spying on members on the public.''

The secretive department refused to say how it became aware of the material on Ms Powell's Facebook account but said there was no political motivation.

The department said it had no problem with "discourse" on politics or policies, and it confronted Ms Powell over an "offensive" remark about one of its public servants.

Responding to the allegations from the activist that it was monitoring her Facebook page, Immigration said it would be "inappropriate" to publicly disclose how it became aware of the post but pointed out that the material was open to public viewing.

Written questions from Fairfax to Immigration about its social media monitoring were referred to the office of Immigration Minister Scott Morrison, which did not respond.

Melbourne-based Cubit Media Research, which can track 24 million social media ''pieces'' an hour, has two contracts with the Department of Immigration and Border Protection to deliver ''media positioning analysis''.

But Cubit's founder and chief executive Warren Weeks said his company was hired to gauge Australians' perceptions of different policy areas and not to track the activities of individual social media users.

''You have to be respectful of an individual's privacy,'' Mr Weeks said.