Overriding screenshare in iChat

[jk000]

Hi I was in a screen share with a friend for the first time the other day using Apple's own iChat, when my friend was sharing my screen I wondered if there was any way I could override what they were doing, other than using the keyboard, using shortcuts to quit the application. Is there anyway that only I can control the curser, or override it, I'm afraid at some point a friend may open some files I wouldn't want them to if you know what I mean.

Thanks