Microsoft fixed the copy-on-write bug in Outlook for Windows in Exchange Online. The fix stops users removing attachments from sent or received messages. A strong case can be made that the fix should have been present from the start to stop any possibility that clients could comprise Exchange Native Data Protection. Microsoft doesn't think many people were affected and they could be right, but that doesn't make the problem any easier to swallow.
https://www.petri.com/outlook-flaw-fixed-exchange-online
