Helsinki police have opened an investigation about the cyber attack on Finnish news agency STT last week, the law enforcement agency announced on Monday.

The case is being investigated as a data system break-in and interference in a computer system, according to police.

The agency announced on Friday that it had taken some of its systems offline following a malicious attack the previous night. It said the attack caused extensive damage.

As the firm initially announced the situation last week, Panu Tuunala, STT's managing editor, said the agency has been upping its preparedness to deal with potential cyber attacks.

In addition to the police, STT also filed reports with the National Cyber Security Centre and the Office of the Data Protection Ombudsman, due to the possibility that a data breach also took place could not be ruled out.