iSentia, a media monitoring service, announced to the Australian Securities Exchange on Tuesday it had been the target of a cyber attack. On Friday morning, it announced a trading halt ahead of an announcement early next week suspected to be in relation to the attack.

The company confirmed the incident affecting its Mediaportal service was ransomware - a style of cyber attack which grabs the affected data, encrypts it and threatens to publicly release it unless the company agrees to pay a large sum of money.

The Australian Signals Directorate's Australian Cyber Security Centre has said it's aware of the incident and has offered technical assistance and advice.

It's not known what data has been captured just yet but various government departments have confirmed their access to the service has been disrupted or limited.

The Department of Agriculture has said it has continued to use limited services and has been informed there is no evidence client data has been compromised in the attack.

In the first week of October's estimates hearings, the Department of Agriculture confirmed it had spent more than $150,000 on media monitoring to iSentia between July and mid-October.

The Attorney General's Department, the Department of Foreign Affairs and Trade, the Department of Education, Skills and Employment and Department of Social Services are also among the departments affected by disrupted services.

The Department of the Prime Minister and Cabinet and the Prime Minister's Office said they don't use iSentia while the Department of Home Affairs said it was aware of the incident but did not confirm it was using the services.

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Media monitoring services are used by a number of Australian government departments to funnel the internet for discussion and media surrounding their department into digestible summaries.

Reports and alerts are then provided to media teams as well as senior management to keep them across the big issues affecting their area of interest.

In order to offer these services, media monitoring services need the contact details for a number of department employees, including senior figures, as well as potentially sensitive information on strategic priorities. It's not yet known whether these details have been captured by the attackers.

An investigation by "leading external cyber security specialists" hired by iSentia is now underway to confirm the extent of the incident.

"iSentia is taking urgent steps to contain the incident and conduct a full investigation into what happened and how to avoid a repeat occurrence in the future," iSentia's chief executive Ed Harrison said.

"Our priority is to restore full service as soon as possible but until that occurs, we have to put processes in place to support our customers."