Why are they tracking me?
But why are they doing this? And is it something to really be worried about?
The reason Google makes as much money as they do isn't because of their search engine (although it's the best). It isn't because of GMail (although that's good). It isn't because of Android (although that's good).
It's because Google is an advertising company. And they are popular with advertisers because the advertisers can target their adverts very precisely. The same goes for Facebook - they are an advertising company and the advertisers can specify exactly who they want to see their ads - down to "interested in spoon whittling" or "fan of Doncaster Rovers".
They do this by building up a profile of you - looking at your behaviour across lots and lots of websites and figuring out what you're interested in. That fingerprint I mentioned earlier.
That, by itself, isn't so bad. Creepy maybe, but not bad.
The problem is it's not just advertising. These profiles can be used to predict what you're going to do next.
The most famous example isn't online at all - Target, a store in the US, had a loyalty card that tracked your purchases. A man found out his daughter was pregnant when Target started sending him maternity promotions - because she changed the moisturiser that she was using. That was from a loyalty card in one store.
Imagine what they can predict about you from everything you do online.
And then imagine what could be done by the bad guys if the collecting companies got hacked. Or, if the government decided that this profile information and associated predictions should be used to prevent "undesirable" behaviour. Yes, it's hypothetical. But once the data is collected, it's not likely to be thrown away.
Take action: If this bothers you, switch to Firefox or Safari as your browser. Switch off location services on your phone. Be wary of the apps that you install on your phone, and check their permissions. And install an ad-blocker.