Third-party cookies are cookies that are set by a website other than the one you are currently on. For example, you can have a "Like" button on your website which will store a cookie on visitor's computer, that cookie can later be accessed by Facebook to identify visitor and see which websites he visited. Such cookie is considered to be a third-party cookie.
Another example would be an advertising service (ex: AdSense) which also creates a third-party cookie to monitor which websites were visited by each user.
Identifying third-party cookies
You can check if website uses third-party cookies in any modern browser. Instructions vary in different browsers, here is how you can do it in Chrome:
- Press F12 to open Developer Tools (or right click on the page and choose Inspect Element)
- In Developer Tools choose "Application" tab
- On the left double click "Cookies" section to unfold it
You should see current website domain (or subdomain) here. If you can see any other domains in this list, this means website uses third-party cookies:
Follow the instructions to block any kind of third-party cookies