The website of the Finnish Parliament was inaccessible on Tuesday afternoon due to a denial of service attack.
A Russian hacker group calling itself NoName057(16) claimed on their Telegram channel to be behind the attack.
"We decided to make a 'friendly' visit to neighbouring Finland, whose authorities are so eager to join Nato," the group said.
The denial of service attack started on Tuesday around 14:30. By 10 pm, the website was back to normal.
Parliament said they are working with the National Cyber Security Centre and service providers in order to restore the website.
The same Russian hacker group has also allegedly carried out cyberattacks on state institutions in Poland, Lithuania and Norway.
On Wednesday morning, the NBI said it had launched an investigation into the interference. The agency said the attack originated from dozens of IP addresses scattered around the world, without providing more detail.