Investigation of VPN Security Vulnerabilities consisting of a survey of the core VPN technologies, Penetration testing of an IPsec based VPN (using Ike-scan and psk-crack), MitM Attack on PPTP based VPN (using ARPspoof, chap2asleap, CUPP2 and ASLEAP) and research of IPv6 Leakage and DNS Hijacking in VPN.