It would be helpful to know what sort of ad network was being used, in terms of the content of the ads (teeth-whitening vs. mainstream advertisers) and what sorts of targeting/segmenting (if any) was done based on variables like domain/location, browser and OS type, etc.<p>As for whether Microsoft users are more gullible, I think the limitations of IE and the demographic profile of its users relative to Firefox and Chrome could explain this trend.<p>My hypothesis: Microsoft users are more likely to be using older flavors of IE, which do not have as good ad-blocking support or extensions to disable rich media ads.<p>Even on new versions, users may not know how to find or configure the pop-up blocker. In IE8, it's under Tools>Pop-up blocker>pop-up blocker settings. This generates an options window whose first field is for personal whitelists. That's followed by two checkboxes and a drop-down menu listing different levels of blocking. That's not the kind of thing my mom would spend much time digging around for or setting up if she used a PC (I set her up with a Mac mini years ago to reduce the number of tech support calls).<p>For those users who do have PCs and are using IE, I believe they are more likely to see these ads than a Firefox or Chrome user, and therefore are more likely to respond to them, simply because they can't or don't know how to disable ads. In other words, it's not so much about gullibility, but rather how tech savvy they are relative to the people who search out and install Firefox and Chrome.