Well, one of the main reasons for the SP1 upgrade, IE6 and all that is to thwart this kind of thing.

Firewalls are there also to prevent it coming from online....

Back in more innocent times there were little utils one could sneak into someone else's computer to make the screen melt or shatter and all kinds of stuff like that.

These days those aren't seen as funny anymore......I used to have a ton of those.....