The immigration department was alerted to the error on its website by The Guardian, whose Australian edition reported that the vast database contained full names, nationalities, location and boat arrival information.
It said every person held in a mainland detention facility and on Christmas Island was identified, as well as several thousand living in the community under the community detention programme.
The department said the information was never intended to be in the public domain.
"The file has been removed and the department is investigating how this occurred to ensure that it does not happen again."
The Refugee Council of Australia said the breach raised fears that those identified could be at risk of retribution if they were returned to their countries of origin, while family members still in their home nations could face harassment.
"It is unbelievable that a breach of this kind could happen. The information is highly confidential for a reason," the council's chief executive Paul Power told AFP, adding that he had been told the data could have been available for days.
He said the ramifications for people who failed in their asylum bid and were returned could be "huge", with some countries punishing those who fled.
"It runs the risk of putting lives in danger," said Power, while calling for a full explanation on how it happened.
The breach is an embarrassing blow to the conservative government, whose hardline policies to combat people-smuggling and deter asylum-seekers have been shrouded in secrecy.
Labor immigration spokesman Richard Marles said the government had blundered.
"It can't determine what should be made public and what should be kept private," he told reporters.
You’ve reached your limit of {{free_limit}} free articles this month.
Subscribe now for unlimited access.
Already subscribed? Log in
Subscribe to read the full story →
Smart Quarterly
₹900
3 Months
₹300/Month
Smart Essential
₹2,700
1 Year
₹225/Month
Super Saver
₹3,900
2 Years
₹162/Month
Renews automatically, cancel anytime
Here’s what’s included in our digital subscription plans
Exclusive premium stories online
Over 30 premium stories daily, handpicked by our editors


Complimentary Access to The New York Times
News, Games, Cooking, Audio, Wirecutter & The Athletic
Business Standard Epaper
Digital replica of our daily newspaper — with options to read, save, and share


Curated Newsletters
Insights on markets, finance, politics, tech, and more delivered to your inbox
Market Analysis & Investment Insights
In-depth market analysis & insights with access to The Smart Investor


Archives
Repository of articles and publications dating back to 1997
Ad-free Reading
Uninterrupted reading experience with no advertisements


Seamless Access Across All Devices
Access Business Standard across devices — mobile, tablet, or PC, via web or app
