I haven't got any porn site software on my computer and have not opened any unsolicited emails honestly. It's purely happening at the Dahon site. It happens randomly when clicking on one of the pages and intermittently and doesn't repeatedly do it. You'd have to click around the Dahon site for a while and then you may get it happen. It's very strange and happens on no other sites. It's like a very subtle hack. This was the link I followed from google that had it happen.
DAHON Curl i3 - DAHON