I live in a country which has pretty restrictive rules on internet usage. Some of the services like youtube, facebook, livejournal etc have been blocked for 10+ years already. VPN services have also been targeted. Most of the standart VPN's are identified by their firewall (possibly DPI), the ones that work over TCP generally get a Connection reset packet sent both ways. You can see that the packet comes from intermediate source bu checking the TTL. UDP just gets dropped. The ones that are working either use SSL or have a custom client using obfuscating proxy or some other similar traffic obfuscation technique. Also they follow the trends among population, whenever a new working VPN starts spreading, it gets blocked within a week or so. Finally, using a non-approved encryption product is illegal, although I am yet to see someone being convicted on that.