You probably knew that there are plenty of spying technologies out there, but did you know just how intrusive they can be at an incredibly low cost? If your girl installs SpyPal on your PC, she'll be able to access your Facebook and email history, log microphone sounds, and even collect screenshots from your machine. Mobistealth will give her the same power over your smartphone. Both products can be had for less than $100, and are just two examples from this large and fast-growing field.
The bottom-line: If your girl wants to get dirt on you, she can. Honesty is probably the best policy, unless you want to find yourself in a espionage arms race with your partner.