For those who don't understand why this happens, consider someone with RealName RN and HobbyName HN.

RN searches amazon for a hat to give as a gift to a relative. FB, Google+, et al. now know that RN bought a hat. 6 Months from now, RN is still getting pop-ups and ads to buy another hat!! That computer has "cookie trails" and MORE stuff that I can't even keep track of anymore that identify RN to other sites.  

Another user, HN, logs in to hobby-Twitter or hobby-FB or maybe even hobby-amazon (to buy a sex toy) on the same computer. Those bits and bytes are cross contaminating. Before you know it, your relative, whose info you put into your gift hat order, gets connected by cookies and Big Data cross referencing to you and your accounts and is being friended by someone else's Hobby FB or Hobby Twitter!  

You can set every setting to the highest level of privacy but it is NEVER 100% privacy.  Cortana is now hard wired into Windows 10 and you cannot get rid of it.  FB, TW, IG, G+, LinkedIn and others have designed their systems to OUT YOU.  And they will, eventually.  

If you have a dedicated computer that you use exclusively for Real Life and another that you use exclusively for Hobby Life, you can better protect your dual lives. But I would not be surprised if they are tracking ISPs and your internet connections.  RN/Real-PC is connecting to the internet via Comcast 123.456.789.012 which is known to be located in on your street in your neighborhood / city / state.  HN logs in from a different Hobby-PC using the same internet connection (Comcast 123.456.789.012).  I would not be surprised if FB, TW, IG, G+, etc. are picking up on that. RN pays the electric bill on Real-PC and I would not be surprised if HN on Hobby-PC started getting ads to switch to another electricity company.  

BE CAREFUL OUT THERE