You may have legitimate reasons for keeping a tab on individuals. You may be looking out for them Or you could be protecting your interests. Nevertheless, your relationship with the person you’re spying on may be damaged forever if they find out. 

That’s why stealth matters.

A parent could spy on their children to protect them. Children are naturally rebellious and don’t like being supervised. If you do it openly, they find ways to shake you off. Sometimes spying is the only way to protect them.

Another ethical example of spying is employee monitoring. If you’re an employer, you can check to see if your employees are loyal to you and not in collusion with the competition. You could also monitor employees to keep up productivity.