Norway's Altinn portal had to be closed after users got access to data belonging to two people, and on Thursday the site remained down.
The Altinn portal is used by Norwegians to access their tax returns, among other documents. The portal is also used by 455,000 companies, which can view VAT (value added tax) statements.
On Thursday, at noon Central European Time, visitors to the site were greeted with the message: "We are continuously working to solve the problem, but are unfortunately not able to give any exact time for when the page will be available again."
The data leak happened on Tuesday when a person accessed his Altinn account. Afterward, as other users logged in, they were able to see his and his wife's name and ID number, according to the Brønnøysund Register Center.
The information was available between 6:17 p.m. and 6:34 p.m. local time, after which the portal was taken offline, the register center said.
On Wednesday, the register center said that it was still working to ensure that the portal will work correctly when it eventually comes online again.
The downtime has consequences for people who haven't checked their tax return, according to the register center. But the greatest consequence is for professional users who are unable to use the portal.
While what happened is serious, the register center also deserves some credit for reacting quickly and shutting down the site, according to Ove Skåra, communications director at the Norwegian Data Inspectorate.
The Altinn portal is no stranger to controversy, and has suffered from both downtime and slow access since its inception.
On Wednesday, the Norwegian Ministry of Trade and Industry presented a report that pinpointed problems with the portal's test regime and ability to handle large loads.
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