I used to play with and spy on my younger sister
Why did you do that to your sister, and how old were you at the time?
I was 8.  I wanted to know something about her, but she wouldn't tell me, so I spied on her.
It's wrong to spy on others and invade their privacy.  Your sister might have had a good reason not to tell you things, and you should have respected that.
I had a right to know.
Your sister's business was personal and private and you keeping tabs on her was not correct. Your actions were a breach of her trust and if you continue this type of behaviour in your adult years, you will alienate everyone around you.