I thought this was the most relevant place to post it... FBI's Secret Spyware Tracks Down Teen Who Made Bomb Threats Interesting, privacy invasion? Yes. For a good reason? Not too sure...
That's the fine line. At what point does it become invasion of privacy? If someone is acting suspiciously, don't you want the authorities to look into it? Plus, in the wake of incidents like the Columbine shootings, do we want to simply ignore someone who's acting suspiciously. Let's say they thought he was doing something and find out that he's not a threat. No harm done. However, if they have the capability to check something out and don't, what kind of uproar would there be if this kid actually did go and blow up that high school? I understand the privacy issue, but at the same time do we want to let someone acting suspiciously just carry on? Do we want the police to wait until someone has committed a crime instead of checking out suspicous behavior?