Secure private chat rooms

[CoolBee]

Anyone got any recommendations?
At the moment I use Yahoo or Windows Live messenger chat for coaching (I do mainly instant messenger coaching). I'm thinking of upgrading to a more secure and more anonymous service (by which I mean if someone hacks a client's messenger, they won't see any details of our chats).
One of the plus points of instant messenger is the ability for the client to have a complete transcript of the session so I need that facility.

Here's what I want:

A private secure chat room service where I can create temporary private spaces for myself and a client who will be invited by email to join and where I or they can keep a complete transcript.

It is best if it runs on javascript so noone has to download any software.

Also, need to be able to clear chat history and not have it saved for eternity on a remote server!

Anyone got any suggestions?

I looked at Chatzy but they don't appear to have any contact email address (leastwise that I can find on their site!) which I would also want in case of problems and also their faq doesn't answer the 'complete transcript' question. I used one of theirs earlier this year for an online funeral and was sad that they only stored the last page or so of chat but didn't tell you that until AFTER you had been going a while.

Otherwise, they would probably have fitted the bill.