Security always must thought of in reference to 'security against what (or whom)'. Opera's VPN and its encryption can hide your IP address and data traffic from snooping along the Internet connection path or the end-target website, but that might better be described as a privacy enhancement (unless one lives in a nationally Internet-censored land, in which case privacy in communication can indeed be a security issue). If one uses a VPN, however, the DNS functions ought to be part of the VPN service for maximum privacy (or security). There are those who would argue that using Google's DNS service is tantamount to abandoning privacy (given Google's massive penchant for marketing all kinds of usage data), but that's probably an exaggeration given that the usage data they market is normally anonymized.