Bear in mind that spyware and adware are programs that install themselves on your computer and monitor/advertise. An unblocked popup is just that: a popup website that has managed to dodge whatever popup-blocking filters Safari uses.
Short of a major breakthrough in hacking around the time-tested UNIX security structures, the only way spyware can get installed on your Mac is if it tricks you into installing it first – “Free Mac optimizer program! Install me now!”
It’s not spyware or adware. It’s Javascript. The little fuckers who write ads are using Javascript now because of the success of popup-blocker technologies. You can turn off Javascript and not see these ads, but lots of Javascript-dependent functions you may actually want on some sites will disappear along with them.