A VPN detection can help you bypass censorship, network firewalls at your work or school, or just get around geolocation restrictions that prevent access to some content. For some, it’s even essential for online privacy and security.

Detecting VPN usage is not easy, since VPNs are designed to conceal their users’ true IP addresses. This means detecting VPN usage requires methods that only work on live traffic under the detection system’s control and can’t be used to identify historical or cached data (or “stale” data) from past connections.

Some common methods for identifying VPN usage include analyzing the MTU of incoming packets to see if it’s larger than a standard value, checking for signs of DNS leakage (e.g. the timezone configured on a user’s browser versus the IP address associated with their connection), or looking for inconsistencies between a device’s geolocation and the last time they accessed web content via a VPN (or proxy).

Top Features of a Reliable Proxy Detection API

Another popular method of identifying VPN usage involves port scanning, which involves actively probing a user’s devices for open network ports that could reveal the presence of a VPN or proxy service. However, this technique raises serious privacy concerns, since it involves intrusive actions on a user’s system without their consent and can misidentify VPN users for legitimate reasons such as corporate network setups or firewall configurations. As such, this is not a reliable or trustworthy method for detecting VPN use. Moreover, it’s prone to false positives and may result in blocking of innocent users.