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The Privacy Commissioner and the Immigration Department have launched investigations into how details of thousands of asylum seekers in Australia were inadvertently made accessible online.

The breach could potentially lead to asylum seekers who were previously ineligible for refugee status having their claims validated, one legal expert says.

Refugee lawyer David Manne said the law was ”crystal clear that identification of a person seeking protection can result in them being granted protection on that basis itself”. ”It’s a fundamental principle of refugee law that a person seeking asylum should be free to make their claim free of disclosure of their identity to the authorities in their home country,” he said.

Mr Manne described the revelation as one of the most ”grave and dangerous breaches of privacy in Australian history”.

The Guardian Australia website reported on Wednesday that the personal details of a third of asylum seekers held in Australia – making up about 10,000 people – had been revealed on the Immigration Department’s website.

Privacy Commissioner Timothy Pilgrim announced on Wednesday afternoon that he had spoken with Immigration and had ”been assured” that the information was ”no longer publicly available”. Mr Pilgrim said he would investigate how the breach occurred. He said Immigration would provide a detailed report about the incident as part of the investigation.

Later on Wednesday, Immigration Minister Scott Morrison released a statement confirming that an ”immigration detention statistics report” released on the department’s website on February 11 ”inadvertently provided access to the underlying data source used to collate the report content which included private information on detainees”.

Mr Morrison welcomed Mr Pilgrim’s investigation and said Immigration Department secretary Martin Bowles had also tasked KPMG with reviewing how the breach occurred, with an interim report due next week.

The Immigration Minister said the ”unacceptable incident” was a ”serious breach of privacy” by the department.

Despite the federal government’s insistence about the need for greater secrecy when it comes to immigration and border protection, the full names, nationalities, location, arrival date and boat arrival information were reportedly revealed on the department’s website.

Refugee Council of Australia president Phil Glendenning said the release of asylum seekers’ information was ”outrageous” and unprecedented.

”We are deeply disturbed by this,” he said.

Mr Glendenning said the breach ran the risk of exposing people who were already vulnerable to ”very serious danger”.

This not only included reprisals if asylum seekers were sent back to their country of origin, but threats to their families – either in home countries, or countries in between.

Labor immigration spokesman Richard Marles said the breach was an ”enormous concern”. ”Let’s be clear – this is a government with a culture of secrecy but it is utterly unable to manage secrecy,” he said in Canberra.