I'm thinking of installing spyware software on my girlfriend's computer.
Why do you feel the need to spy on your girl?
I wish to know her dark secrets.
In general installing spyware is bad, but doing it to your partner is particularly awful. You should learn to trust them if you want your relationship to work in the long run!
Being a hacker doesn't make it bad. I should be able to know what she's hiding.
If you think that she is hiding something, you should try to talk to her about it. You should not try to spy on her using software.