Visiting websites is pretty simple. You go to a URL, and your browser loads the website code into a format for you to easily read. However, many websites have internal links to other websites. For example, if you go to CNN.com, your browser will not only contact CNN.com, but also a number of other websites such as Facebook, Google, and many more. Some of these are legitimate third-party connections, but often they simply grab some extra style information to make the website look better, or include a Facebook "Like" button to allow you to interact with Facebook from that website.
Since you are also contacting other websites when you go to a website, you give them the same amount of information as you give the website you are directly visiting. This information includes your IP address, header information, and some other basic data. This can be bad, since this data can be used to tell who you are by other websites, but it is more devious than that. Many of these third-parties also load software onto your computer to run while you are visiting the website. Often this software gathers more information about your computer (e.g. browser and operating system versions, screen resolution, etc.) and how you use the website (e.g. what links you click and how long you stay on the site) and sends this information back to the third party.
You make think that a website like Facebook or Google only knows what you are doing online when you visit their respective websites. That is inaccurate, since many other websites also contact Facebook, Google, and many others when you visit them. This gives these companies even more information about your browsing history than you generally even consider.
Information collected this way:
- What websites you visit
- How you use a website
Who does this:
- Many other advertising agencies
To prevent this kind of tracking of the websites you visit, there is one main option: block known bad third-party software from loading when you browse the web. There are small programs you can install in your browser which will use a blocklist to disallow certain third-party code from running on your computer.
Some browsers already block third-party trackers automatically, without an extra extension, including Firefox and Brave.