I wrote this one for Facebook friends - reposting here. The TidBITS review is excellent.
This is roughly how things work ...
- Someone in your home visits a certain web site.
- Your home internet provider (ex: Comcast) associates that site with the identity of the Comcast account holder. They sell that information to the universe. Facebook buys it.
- Facebook shows the Comcast account holder ads based on the visited site.
This happens because your internet provider is your default internet directory service (DNS provider) - Comcast knows all the sites you visit and (as best we can tell) they sell that information.
It's basically an internet design flaw.
If you're a bit geeky you can change the DNS settings in your home router to someone more trustworthy than Comcast (which would be anyone else, really). In our home that's an Apple Airport. I have our settings below but your settings will vary.
Cloudflare: 126.96.36.199 (their 188.8.131.52 address doesn't work with some ISPs)
Quad9: 184.108.40.206 (as backup)
For more information see an excellent TidBITS review. If you truly want privacy, particularly on iOS where DNS settings are a pain, you need to use a trustworthy VPN (see below).
PS. It’s easy in macOS Location settings to experiment with different settings. This is particularly important for a laptop that moves between locations. On my standard macOS Location I use Cloudflare, then Quad9, then Google. Sadly iOS DNS settings are a mess (per TIDBits):
In iOS, DNS server settings tend not to work the way most people would want them, which is as in macOS: setting the details once and having them work on every network to which you connect. The settings have to be set for each network. Worse, we’ve found in our testing that after changing DNS values, the settings revert to Automatic and the server IP addresses we entered are tossed. There’s also no way to set DNS servers for cellular connections.
In iOS you need to use trusted (not free!) VPN provider. I use TunnelBear’s free GB option, I wish I could buy blocks of data from them rather than yet another subscription. If you use a limited data capacity VPN on a Mac you should use TripMode to reduce background data use.
Update 4/22/2018: A Gizmodo article reminded me why this DNS control is more important now ….
“The FCC under Chairman Pai changed the rules in the United States for ISPs allowing ISPs to start selling your browsing history to target advertising against you,” Prince said…
They mention two popular VPNs - ProtonVPN and Private Internet Access. Curiously PIA claims TunnelBear does not protect me — which makes me a bit suspicious of PIA.