How did Facebook legally get all my contacts?

I signed up a Facebook account, Used my company email address, said "no" to searching for recommendations for friends based on my email address book.... with no friends added, Facebook now suggest all my clients, and everyone i have ever sent an email to who also has Facebook to be a friend! how in the world did Facebook manage to figure out all my email contacts? is that even legal? my customers base is absolutely top secret to me, does this mean anyone can figure out who i email? I have my own company domain, this isn't just a Yahoo or Google free email account. Now does that also mean Facebook will connect my customers with each other as possible friends?

Nice work Facebook! see yah! will never sign up for that again u hacks! I must say, i was amused when i choose to delete my newly created Facebook, it takes many weeks before they will just "in case i change my mind!" Even if you don't have any answers to this, has anyone else been this annoyed with Facebook? share it. As far as I'm Concerned, if someone else on the internet sees my address book, they are hacking me to get it