Have you ever wondered after searching online for a certain item, say a new TV, why you suddenly see more online ads for TVs? Or after you’ve visited a website, you notice more online ads for that website.
The reason you saw those targeted ads is because a lot of websites track your behavior on their sites. They may collect information about you, and they may even sell all of that data they’ve collected from you.
To help avoid this, one of the tools I use is Ghostery.
Ghostery is supported on all of the major browsers and currently blocks over 1900 trackers.
Just keep in mind it does interfere with things like Facebook like buttons on non-Facebook pages, as well as other social buttons. This can be tweaked in the preferences. Personally, I block it on all but a few white-listed sites for this reason;
If you’re logged into Facebook and visit a website with the Like button or another social plugin, your browser sends us information about your visit. Keep in mind that Facebook isn't retrieving this information. Since the Like button is a little piece of Facebook embedded on another website, the browser is sending information about the request to load Facebook content on that page.
In other words, if you simply visit a website that has a Like button on it, Facebook knows you visited that page if you’re logged in to Facebook (uncheck “Keep me logged in” before logging in to Facebook). And it isn’t that they know somebody with a Facebook account visited that page and it had a Like button on it. They know you visited that page because you are logged in to Facebook and that information is available to that pesky little Like button.
I didn’t mean to turn this into a Facebook rant, but there ya go…
Get Ghostery and get some control over who has access to your online behavior.