An explanatory email from PlusNet told punters: "At the time of making this change the engineer had two management console sessions open \ufffd one to the backup storage system and one to live storage. These both have the same interface, and until Friday it was impossible to open more than one connection to any part of the storage system at once."

"The patches we installed on Friday evening removed this limitation, but unaware of this, the engineer made an incorrect presumption that the window he was working in was the back-up rather than the live server. Subsequently the command to reconfigure the disk pack and remove all data therein was made to the wrong server."