State and federal government agencies are increasingly outsourcing to private contractors to investigate and conduct surveillance on welfare and work-related claims, including through monitoring social media.

On Wednesday the Daily Telegraph reported the Department of Human Services had been gathering evidence from social media accounts and other online accounts in relation to cases about false Centrelink payment claims.

The department had been using information from accounts to debunk claims. The Daily Telegraph reported that in at least one case, posts from a Twitter account were used to prove two people who were claiming welfare as single people were in a relationship and had announced a pregnancy together.

Federal contracts showed a series of agreements with private investigators to conduct “security surveillance and detection” on behalf of the department.

Many of these contracts were for the primary purposes of conducting “optical surveillance”.

Questions have been put to the department about which organisations are conducting social media monitoring, and how much the department pays for these services.

But there is a broader trend across government to rely on private contractors to investigate claims of fraud or workers’ compensation claims.

NSW tender documents also show that Workcover NSW took on some of the same private investigators as the Department of Human Services to conduct surveillance on their behalf. Workcover NSW commissioned more than 10 private investigators from 2015-18 to assist them in conducting investigations and surveillance into Workcover claims. The contracts were worth more than $3m.

The use of social media analysis – or “open-source intelligence” – is a growing and lucrative field for private contractors, but has raised the concerns of some privacy advocates.

The Department of Human Services said it had discovered more than $2m in fraudulent claims through social media monitoring.