Look back at them in order to let them know that bạn are aware that they are looking at your computer screen. If this does not work, then ask them 'what is the matter/problem?' or.. 'Why are bạn looking?'
Well, I: - Change tabs - Tell the to stop! - Close the tab - Glare (If it's my mom who suddenly pops up to 'spy'...That's really irritating!! >.< I can't even tell her to quit it: she'll get suspicious!! -sulk-) - Stop working /doing what I'm doing (If they're being really annoying and nosy) - Get pissed and turn off the computer and go (if they're TOO persistant and nosy)
...Honestly! -defeated sigh- Don't these people know the meaning of the word called "privacy"??! ... hoặc about how utterly annoying and distracting what they do is??! X( ~ssu!