I was looking for a tablet from my home PC on Amazon and sometimes I find Amazon ads on Facebook which contain suggestions related to my search criteria; I never worried too much as I thought the Amazon ads were just frames to their website which can access my cookies and recognise me.
I started worrying when I saw the same Amazon ads from my office PC where I never logged into Amazon and I never searched anything. Is it legal for Facebook and Amazon to share my data?
I never mentioned a tablet in my Facebook conversations so Facebook itself cannot have processed my preferences and built the ads.