In a Windoze 7 box, after going into Control Panel/Devices/Imaging/(the webcam), then right-click, drill to "disable" and click, can the webcam be remotely activated?
The action above changes a Registry value, so any attempt to turn the webcam back on would have to come via a Trojan which could change Registry values, right?
My antivirus alarms on all such attempts which do not come from the Administrator, and requires my approval to permit the change, so I'm safe, right?
Of course, a low-tech solution may be best: grab some blue masking tape and cover the webcam. If you need to use the cam for a video conference, pull off the tape and replace it when the conference is over. The same goes for those TV webcams, or any wireless/networked security cams on your property, all can be intercepted by the gummint or your neighborhood pervert. It costs $1500 to hardwire 4 exterior security cams but they can't be intercepted unless/until you put them on the 'Net.