Where Did Capital One Get My Information?

I've been struggling with the Capital One promotional letters for months. I still did not figure out where they got my contact information and send me the annoying credit card mails. Did you have the same problem before? Got spammed by some company you have no idea about?
This is what I learned from Leah Betancourt's post---How Companies Are Using Your Social Media Data? It is almost incredible how people's conversation over the social networking sites are documented and used for some business reasons. Can companies do that without violating media ethics and all? I knew that Google used your emails to determine what kind of ads to put on to each individual's gmail page, but I don't see things this worse coming.
I think I know why my information was acquired by Capital One. My facebook account, my twitter, and LinkedIn, they are selling me to strangers with business agenda. I hope y'all won't encounter similar problems. So why don't we take a look at some of the tips Leah Betancourt offered? 

1. Determine whether you want to go public or private with your social media profiles. I

2. Eliminate people and sites from your social networks that you don’t need.

3. Pay attention to your friend, invite, and connection requests.