Imagine your email software has this feature:
As you are reading an email you are corresponding with person A, there is a button. By clicking it and selecting another person B, all the emails you have with person A in the past are immediately forwarded to person B, without warning.The email forwarding is executed virtually. Instead of physically forwarding each mail one by one to person B's mail server, basically your mail software gives access to Person B, at his own leisure, to browse EVERY of your email with person A. If you had done this by mistake, there is no process to cancel because the "forwarding" process is complete the moment person B is selected. There is no Undo option. You can scream and run round the room, but person B will continue, at any time in the future, to be able to read EVERY single email you had with person A.
If you are a careful person that would never do such a silly thing, person A could click the Add button and the outcome will be exactly the same.
The above is essentially what Facebook chat is about.
The moment a conversation participant Adds someone (can be anyone that pops up in the auto-complete list when you type some characters) to a conversation, that person has read access to every single message in the existing conversation back to the very first message, which could have been written many years ago. There is no cancelation option. The beautiful thing is the the person newly added can take his time to browse through your entire conversation, any time in the future, from any computer, by simply logging in to www.messenger.com. No other software or app is necessary. There is no time expiry.
A touch of finesse is that if you, in a moment of panic or frustration, delete the entire conversation from your account, that person can continue to read ALL the messages, while you are now locked out! The Facebook chat delete function is to remove the person performing the delete operation from a conversation, not the other persons in the conversation. Sweet, isn't it?
Don't worry, there is no one to call for help, because there are no phone numbers available.
Facebook support persons helpfully explain that Adding is like forwarding email. Like email, you cannot retract an email once it's forwarded. The slight difference is that you are not simply forwarding an email, but the complete Inbox, Sent folder, offline folders, archive folders, backup folders, etc.
If you are in a group conversation, whether it be private family matters or confidential company plans, anyone in the conversation, intentionally or otherwise, can just simply Add another party and the damage is done, COMPLETE, courtesy of Facebook technology.
When you Add a person to the conversation, the following warning message is missing:
By Adding xxxxx, you are authorizing her to read every existing message in this entire conversation. She will be able to read all of them even if you Remove her from the conversation in the future. Warning: there is no Undo function and the release of messages is irreversible. If this is not your intention, click Cancel to abort.It is a simple matter to remove a person from a conversation's access list when he/she is Removed from the conversation, so that the damage can at least be limited to a few pagefuls. But maybe the Perl language used at Facebook has some limitations.
You have been warned.