There are a large number of ways to unmask visitors using a vpn or even tor, you can use dns requests to do it, javascript, vpn log access, isp access, cookies,

There are a large number of ways to unmask visitors using a vpn or even tor, you can use dns requests to do it, javascript, vpn log access, isp access, cookies, browser history, search queries, time attacks, webrtc, google chrome, ads...