"Anonymous Finland" claims it has compromised the email logins and passwords of 500,000 Finns -- about ten percent of the country's population.
Among the hacked emails are allegedly accounts belonging to journalists at Finland's mainstream daily Helsingin Sanomat, members of the Finnish parliament, police officials, Helsinki city councillors and students and faculties at several of the country's universities.
The hackers said they had taken advantage of security loopholes in company computer systems storing email addresses and passwords.
Anonymous Finland has also launched a campaign against the rightwing extremist Finnish Resistance Movement, leaking a list of its membership applications on October 31.
And on Monday, the group announced it was launching a series of cyber attacks against Finnish mining company Talvivaara, alleging its mining activities in Sotkamo in eastern Finland are conducted to "the detriment of the local natural environment and people of the communities".