User identification methods used by social networks and which can be used by any websites, in general, are the following:
Browser information:
-UserAgentand navigator settings. This is a text line used by client applications (in our case it is the browser) as their name. It includes several components.
-Screen resolution and visible area.
-Plugin set.
-Other changeable parameters.
Storage:
-ETag
-Web storage
-IndexedDB
-Web cookies, LSO Cookies, Evercookies
-HTTP Strict Transport Security
-History API
Link-type and location:
-IP address (Proxy) -Domain Name System -WebRTC -Geolocation -Timezone