Apparently this was at a level equal to TS/SCI.

Defence Forces file criminal complaint over newspaper's intelligence story

The Finnish Defence Forces' Defence Command has filed a criminal complaint regarding the disclosure of security intelligence data to Finland's most widely-read newspaper, Helsingin Sanomat. The paper featured a story on a top secret intelligence research centre on Saturday
Rationalization by the editor.

Esa Mkinen, editor at Helsingin Sanomat, explained in a column late Saturday afternoon that the newspaper decided to make the data public in line with its primary duty to inform.
"The most important task of the media is to monitor and control the activities of the authorities. HS is responsible for supplying its readers with sufficient truthful information about what is happening in society," he wrote.
The editor makes the case that the residents of Finland, and even its MPs, know very little about the centre that was reported on in the article, and so the paper felt compelled to share the data it had obtained.
Mkinen wrote in his column that "if you want to say more than the official data, you have to rely on classified information".