The National Cyber Security Centre says that it is aware that the email systems of at least a dozen organisations in Finland have been hacked, and that hundreds of corporate, municipal, and other group email services are at risk.
The centre issued an updated warning on Monday (in Finnish) that a critical vulnerability in Microsoft Exchange email servers is being targeted by active exploitation.
Experts believe that worldwide the email systems of tens of thousands of organisations have been hacked. Juha Tretyakov, a specialist at the National Cyber Security Centre told Yle that the scale of the problem is the largest seen in Finland for at least two decades.
The centre has advised system administrators that a simple update to servers is not enough to deal with the intrusion, and it lays out other measures needed to upgrade security.
The situation does not require action by individual users.
While Tretyakov said it is already certain that the email systems of at least a dozen organisations in Finland have been hacked, the Cyber Security Centre has not taken a position on who or what entities may be behind the ongoing intrusions.
"It's up to the police to find that out," he said.