From Lawrence Abrams' 24-Jun-2021 BleepingComputer article WD My Book NAS Devices are Being Remotely Wiped Clean Worldwide:
Today, WD My Book owners worldwide suddenly found that all of their files were mysteriously deleted, and they could no longer log into the device via a browser or an app...Owners reported that the MyBook logs showed that the devices received a remote command to perform a factory reset starting at around 3 PM yesterday and through the night...If you own a Western Digital My Book NAS device, it is strongly advised that you disconnect it from the network until we learn more about what is happening....
Update 5:45 PM EST: Western Digital told BleepingComputer that they are actively investigating the attacks but do not believe it was a compromise of their servers. They believe that attacks were conducted after some of the My Book owners had their accounts compromised...
Kudos to Susan Bradley for posting about this yesterday on AskWoody.com at Got a Western Digital My Book?.