Are you seeing files with any of these extensions in your server? – .01, .02, .amnesia, .[Help244@Ya.RU].LOCKED, .CRYPTOBOSS, .[email@example.com].SON and .@decrypt_2017. If so, then your server is hijacked.
One of the major ransomware virus that is circulating now is the Amnesia malware. Once infected, it locks up your entire server files and encrypts them in such a way that you can no longer use them.