I support IT systems for office with 2 workers. Both workers use Macbooks on LAN. The only other things on LAN are router and printer. The only shared login the workers have is a Dropbox account. Worker A does not have a Facebook account. Worker B has a Facebook account. Things Worker A searches for on internet (eg office supplies) promptly appear in Worker B's Facebook ads. I can't figure out how Worker B's Facebook knows what Worker A is searching for. Any ideas?

  • What website is Worker A doing their searches on? And, did Worker A click on an Ad for the searched item?
    – TTT
    Jan 13, 2017 at 22:56
  • Worker A is searching Amazon for office supplies. I've just confirmed that Worker A does NOT click on ads in Amazon.
    – posix
    Jan 16, 2017 at 12:51
  • I've just further clarified that Worker A is searching on Amazon, not Google.
    – posix
    Jan 16, 2017 at 13:12

1 Answer 1


They are using same public ip address I guess. Is quite strange because usually, Google/Facebook shouldn't track your ip for many reasons:

  • Because Ip addresses cannot reliably identify an individual user, advertising services track visitors through small files on their browsers called cookies.
  • When you visit a website that is advertising with Google AdSense, it tells your Web browser to create a cookie with data to identify you as a unique visitor

Anyway, Google's advertising services is a "mistery" how it works and Google change its mechanisms constantly, like for SEO. Is like the "Coca Cola's secret". I've been in courses about SEO and they teach to you a lot of techniques to improve it and they work, but nobody knows 100%. There is always a small uncertainty factor.

So, usually the Ip addresses are don't used to track visitors, but if you are pretty sure this is happening, maybe Google changed something. Maybe they do use a visitor's current IP address to help select ads.

EDIT Yes, I can confirm it. I found this link on Google Documentation. Look at the paragraph which say:

Even if you opt out of Ads Personalization, you may still see ads based on factors such as your general location derived from your IP address, your browser type, and your search terms

EDIT2 Thanks @TTT for your comment. You are right. Anyway, Facebook ads works in similar way like Google ads.

  • 1
    OP is talking about Facebook ads, not Google Ads. Am I missing something?
    – TTT
    Jan 13, 2017 at 20:28
  • IP-only-based personalization would be a huge privacy problem. Your quote also only says that the "general location [is] derived from your IP address". That does in no way confirm that searches on computer A influence the ads served on computer B purely based on the IP.
    – Arminius
    Jan 13, 2017 at 20:47
  • @Arminius I understand from that quoted phrase in documentation that based on IP ads can change. Nobody said "IP-only-based", so no privacy problem in my opinion. Jan 13, 2017 at 21:04
  • "Things Worker A searches for on internet (eg office supplies) promptly appear in Worker B's Facebook ads." is what OP wants to have explained. Your answer seems to suggest that this is due to using the same IP. The privacy implication would be that I could find out what someone using the same IP had searched on the Internet.
    – Arminius
    Jan 13, 2017 at 21:11
  • Hmmmn.... maybe you are right about the privacy violation... here can happen 2 things: A- Or OP is not telling to us all the necessary data, or B- Facebook is doing IP based ads segmentation which as you say could be "reaching the legality". I think we agree in Facebook is doing segmentation by region or zone which is a group of ip addresses... but doing that to final IP is too much... maybe is coincidence because they are on same region... nobody can assure this I think! :) Jan 14, 2017 at 10:15

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