[tryauuum]

from the google translated page of the provider

  What happened?

  It is our best estimate that when servers had to be moved from one data center to another and despite the fact that the machines being moved were protected by both firewall and antivirus, some of the machines were infected before the move, with an infection that had not been actively used in the previous data center, and we had no knowledge that there was an infection.

  During the work of moving servers from one data center to the other, servers that were previously on separate networks were unfortunately wired to access our internal network that is used to manage all of our servers.

  Via the internal network, the attackers gained access to central administration systems and the backup systems.

[rudasn]

Can someone ELI5 how just having network access is enough to do such damage?

Were admin interfaces IP whitelisted only (no other auth)?