Web browser "plug-ins" or "browser helpers" can insert hot links and cause pop-ups. You might have installed one of those as a payload associated with installing a browser or Adobe update or other software update. Those things track your behavior and web sites visited, and they're often not considered spyware because you opted to install it (you might not have realized it because it's often a default that you need to uncheck.

I think of this as click-through abuse, and it's becoming more and more prevalent among major software and website players. You don't own your own information anymore. It's a complete invasion of privacy IMHO.