Sopra Steria says it will take a number of weeks to restore its systems to full operating capacity after confirming an attack by hackers using a new version of Ryuk ransomware.

The IT services firm says the new variant of Ryuk was unknown to antivirus software providers and security agencies. First detected on 20 October, the company says it has made the virus signature available to all antivirus software providers, in order that they may update their software packages.

The company claims that the virus disabled only a "limited" part of its infrastructure and that there was no indication of leaked data or damage caused to its customers’ information systems.

"Having analysed the attack and established a remediation plan, the Group is starting to reboot its information system and operations progressively and securely, as of today," says the company. "It will take a few weeks for a return to normal across the Group."

It did not disclose whether a ransom demand had been paid to the virus' authors.