http://www.techradar.com/news/6-of-the-best-vpn-kill-switches-2017

Once the domain of internet security geeks, VPN (Virtual Private Networking) has gone increasingly mainstream with smart surfers looking to keep their net traffic private, and away from the prying eyes of hackers, governments or overly profit-driven ISPs.

However, remember that VPNs do have some limitations in terms of security, and when using a VPN service, one important step is to perform an IP leak test. This verifies that the VPN tunnel is enabled, and that your real IP address is successfully cloaked by the VPN.