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Pop-up blocker no longer working: Not just Safari, 10.3.8, or Macs

Pop-up blocker no longer working: Not just Safari, 10.3.8, or Macs

Yesterday, in our Mac OS X 10.3.8 coverage, we noted a few reports of users seeing pop-up ads in Safari since installing the 10.3.8 Update, even though Safari's "Block Pop-Up Windows" feature is enabled. Since then we've been buried by reader confirmations of such issues -- one of the most overwhelming responses to a specific issue we've ever had. Based on those responses, as noted below, we've moved this topic into its own article. As we'll explain, the problem appears to be only coincidentally related to OS X 10.3.8 and is not isolated to Safari.

Pop-unders, not pop-ups Our original article, reflecting the reports of readers, called these browser windows pop-ups. Although a few readers have indeed seen pop-up ads recently, the overwhelming consensus of readers is that pop-under ads -- windows that open behind the current browser window -- are the real issue.

Not just Mac OS X 10.3.8 Initial reader reports, covered yesterday, claimed this issue arose with the installation of Mac OS X 10.3.8; however, it appears that this is simply a coincidence -- these "unblockable" pop-under ads just happened to start appearing around the time that 10.3.8 was released. We've come to this conclusion because a significant number of MacFixIt readers who haven't updated to 10.3.8 -- running everything from 10.3.4 to 10.3.7 -- are also seeing these ads. (A MacFixIt computer still running 10.3.5 has also experienced this issue over the past week or so.) We've also received identical reports from users of 10.2.x (Jaguar), and even a few from users of OS X 10.1.x (who are running other browsers with pop-up blocking features -- see below). The incidence of these pop-under ads has been increasing since their apparent "debut" a few weeks ago.

Not just Safari Contrary to initial reports, this problem isn't limited to Safari; subsequent reports have noted pop-under ads victimizing a number of browsers that provide pop-up-blocking features, including the latest versions of Safari, FireFox, Mozilla, OmniWeb, and Camino.

Not just Macs Reader Dan Kelly notes that the issue also isn't limited to Mac browsers: "Recently I have found a similar issue with pop-ups in Firefox on my work PC. It may be that the advertisers have discovered a way around the blockers, rather than an issue with Safari itself."

Apparent new ad technologies Since this issue is not limited to Mac OS X 10.3.8, Safari, or even Macs, it seems pretty clear that the real issue is not the Mac OS X 10.3.8 Update, but rather that Web advertisers have figured out a way to get around increasingly popular pop-up blockers. As reader Sandro writes, "As a web developer I have seen JavaScript workarounds for popup blockers so I?m thinking...that the popup ad makers have gotten wise."

For example, Brian Fountain sent links to two interesting discussions (link 1, link 2) on how to subvert pop-up blockers. The details of these techniques don't seem to describe the specific pop-under ads being described by MacFixIt readers, but the information provides some insight into the trends in Web advertising.

Some ad companies are even bragging about their ability to subvert pop-up blockers. For example, features the following blurb on their home page:

"Due to the proliferation of Popupblockers we have altered our popup code so that if a blocker is detected a layer ad will be delivered. This will increase your overall daily impressions and revenues."

Users report seeing these pop-under ads on many different sites, but in reader email to MacFixIt, the most frequently mentioned sites have been,,, and (We don't mean to imply that these sites are any worse than other sites; rather, the advertisers of these sites appear to be using these new, pop-up-blocker-subverting tricks. Many other sites were also reported, but for whatever reason more MacFixIt readers visit these particular sites and are thus reporting them.)

Why ads don't show up every time a site is visited A number of readers have wondered why these ads don't appear every time they visit a particular site. Other readers found that after trying some trick, the next time they visited a site the ads didn't appear, thus leading them to believe that they'd found a "fix." Note that most of these sites use cookies to determine if you've already "seen" their pop-up or pop-under ads, so once the ad appears, you will not see it again until the next hour/day/week/etc. (whatever time period the site or ad provider have chosen). Some users have misinterpreted this behavior as a reflection that something they've done has "prevented" seeing ads, but the reality is that the site has simply fulfilled its hourly/daily/weekly ad quota for those users.

Avoiding such ads Until Web browser developers figure out a way to block these new ads, MacFixIt readers have suggested a few ways to avoid pop-unders:

  • Disable JavaScript in your browser In our testing at MacFixIt, this does appear to prevent most pop-under ads; however, it also means that you lose desired JavaScript functionality.
  • "Post-date" your cookies Using a procedure that's likely more trouble than it's worth, you can "timestamp" your cookies with a date in the future; because of the way in which cookies are used by advertisers, described in the previous section, the site will thus think that you're not "due" for an ad until the future date. Because this procedure has to be repeated for every site with pop-up ads, we don't feel it's worth explaining -- it takes less time to simply close the offending ad.
  • Use a custom hosts file A hosts file, if present, overrides any DNS server in associating a particular URL with a particular IP address. If you have a hosts file that takes known ad server URLs (e.g., and directs them to your own computer (, those servers will never be contacted and, thus, you'll never see their ads. A number of sites have collected the URLs of known advertising servers and created downloadable hosts files. For example, the Mike's Ad Blocking Hosts file site provides a link to such a file and instructions for installing it (scroll down to "Linux/Unix/Mac OSX").

Safari pop-up blocker still working well for pop-ups Despite all the frustration users are experiencing with pop-under ads, many MacFixIt readers report that Safari's pop-up blocker is still working very well. The true test of its efficacy is to surf with the blocker disabled, or to use a computer that doesn't have Safari. As Roger Steen explains, "I still have a computer operating on OS 9.2.2 with IE, and that has tons of pop-ups coming through when I surf, so I know that Safari is catching most."

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  • link 1
  • link 2
  • Mike's Ad Blocking Hosts file
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