Yesterday I installed SecurityKISS (free) to give it a try. The install went fine and everything seemed to work okay -- with one exception. . . every time I attempted an internet 'search' using either StartPage or Ixquick, I encountered a captcha challenge. And it wasn't a one-time thing -- it happened with every new search What's that all about? By the way, I didn't get the captcha thing when searching with Google, Yahoo or DuckDuckGo.
I'm guessing that StartPage and Ixquick are using some DDoS protection service that has blacklisted SecurityKISS servers. That's not uncommon, for any VPN service, given that jerks use them for spamming, DDoS, etc. Just use a different server. Eventually, it'll probably get cleared. I don't recommend ZenMate or other browser "VPN" plugins. AirVPN doesn't cost much. PIA costs even less.
Never seen that behaviour before. Been using the free version on and off, for a quite a while – plus, use Startpage.com on most browsers (I use multiple browsers) – and, I frequently change servers whenever I use the VPN.