Ok, we are after some remote desktop to do the following:

Client logs into website, clicks button, and we (the support person) have control of their desktop. The software must reside at our end

Does anyone know anything that can do this?

There is some criteria:
* Doesn't matter if it's free or paid, we have some budget if needed.
* It ideally requires no addtional software for the client to install
* It is reasonably easy to set up
* It is secure and not too much of a security risk
* Ideally be able to support multiple sessions (ie more than pair of client/server in their own sessions)

We have used Macromedia Breeze/Adobe Connect in the past, this was quite expensive and also was a bit too much like a training tool. WinVNC was suggested, but it's quite hard to set up and seems to have zero support (perhaps due to it being freeware).

Any other suggestions?