RSplaneta/Shutterstock You have your favorite VPN (Virtual Private Network) app installed on your phone, router, or computer, and it's masking your IP address. That sounds great, but it's not everything a good VPN service should offer. The best employ a combination of strict no-log policies, impenetrable encryption, DNS leak protection, and a dependable kill switch that ensures your data doesn't spill if the connection drops.  Conversely, bad VPNs tend to cut corners — they may log every session, skimp on the basics of internet security, or quietly study your browsing habits and sell your data to the highest bidder. The…