Like nature, advertising abhors a vacuum. There's no reason to assume that future virtual worlds—the fantastic ones we'll inhabit inside headsets like Oculus Rift, or the augmented ones we might espy through devices like HoloLens—will be any different. The moment there's a convincing simulacrum of Mars for you to explore, you can bet someone will be trying erect a billboard inside it.

But new technologies offer opportunities for subversion, as well. "Brand Killer," created by a group of students for the PennApps hackathon, is one such exploration. It's a customized head-mounted display that uses image processing to recognize brands and logos and blur them in real time. Think of it as ad-block for real life. The idea, its creators write, is to make people "blind to the excesses of corporate branding," quite literally.

Right now the apparatus looks like a helmet made out of a disassembled toaster. But as devices for mediating our vision become commonplace, this sort of functionality could become as trivial as adding a few extra lines of code. By then, it could become more essential, too.

In years to come, the boundaries between the physical and digital will continue to evaporate. Both in your web browser and outside it, advertisements will become more personalized and more persistent.

In this future, ad-defeating mechanisms could become a necessary, satisfying countermeasure. Consider the growth of Adblock Plus itself. According to a recent report, in January 2010, it had 21 million users. By January 2013, it had grown modestly to 54 million. But just one year later, in January 2014, the number of people using the software had jumped to 121 million. In other words, the ad-killing industry is enjoying a moment of hockey stick growth.