Immigration was accused of ''spying on citizens'' and monitoring online political dissent after an internet row with a pro-asylum seeker activist last week, allegations the department denies.

But the giant departments of Defence and Human Services and the smaller Department of Social Services have deployed much more sophisticated weapons in keeping tabs on what the public says on Facebook, Twitter, blogs and other networking platforms.

Human Services, which runs Centrelink, Medicare and the Child Support Agency, has developed its own powerful software with the government's science organisation, the CSIRO, that can sort through millions of social media entries and look for interesting items.

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But the department, which has an online media team of 10 public servants, says its Vizie system is not used to keep tabs on the activities of its millions of clients, nor is it an investigative tool to bust welfare fraud.

''The Department of Human Services uses Vizie, a social media monitoring tool developed in partnership with the CSIRO, to identify topics relevant to the department that are being discussed online,'' a spokeswoman said.

''Vizie captures feedback published on publicly accessible social networks about people's experiences with the department and automatically highlights items that may require a response.

''The intention is to identify service issues, information gaps and people who may need help, so the department can provide timely assistance.''

Vizie can also identify threats or abuse against welfare or child support officials but DHS said it did not directly confront offenders, preferring to report them to administrators of the social media sites instead.

''In cases where inappropriate content is published on social media, such as when the privacy of our staff or customers is breached, the department seeks removal through the service provider's reporting function,'' the spokeswoman said.

The Defence Department has also invested in the capability to monitor online chatter about the army navy and air force, using the powerful BuzzNumbers program, which is bought off the shelf and used by the department's 216-strong spin unit.

''The service includes mechanisms for Defence to view the overall number of posts and submissions across various social media channels, and provides a range of reports relating to the volume, nature and content of social media items or submissions,'' the media unit said in a statement.

The Department of Social Services is also using BuzzNumbers but was careful to stress the software was only allowed to be used by trained operators.

''The Department … is currently monitoring social media to gain insight into stakeholder and community views on our programs and policies in order to better service their information needs,'' a spokeswoman said.