Worldclient IM puts user online when user's desktop is locked and someone moves the mouse or touches the keyboard...
... like the cleaning lady.
What I would like to say: that should not happen. When the desktop is locked, the user is not there, and should not be online (unless he's using a remote session of course like when connected through RDP to the machine where WCIM runs on).
Thank you for your suggestion to not change the users IM status while the machine is locked. This will be considered for future versions.
J-M Roth commented
In fact I consider this a bug, but since support does not we'll need to look at it as "improvement" ;-)