Data storage devices maker Western Digital Corp says it is investigating a network security breach that affected some of its systems.

According to a press release published Monday, unidentified hackers gained access to some of its internal systems on March 26.

“Based on the investigation to date, the company believes the unauthorized party obtained certain data from its systems and is working to understand the nature and scope of that data,” Western Digital said.

Due to the incident, the company took affected systems offline and is implementing proactive measures to secure business operations. It is also working to restore impacted infrastructure and services.

“While Western Digital is focused on remediating this security incident, it has caused and may continue to cause disruption to parts of the company’s business operations,” Western Digital added, without providing any further details.

Since Sunday, April 2, multiple users of Western Digital’s network-attached storage (NAS) service My Cloud have been reporting they couldn't access their cloud-hosted media repositories. According to the service status page of Western Digital’s My Cloud cloud storage service, besides My Cloud, the service outage affected My Cloud Home, My Cloud Home Duo, My Cloud OS5, SanDisk ibi, SanDisk Ixpand Wireless Charger.

At present, it’s unclear who was behind the attack. The incident does not appear to have yet been claimed by any major ransomware group.