The online advertising world was all abuzz this week with the revelation that a number of very high traffic websites have been obtaining large percentages of that traffic through pop-ups on other sites. Apparently, by including actual site content in the pop-ups rather than an advertising message, these pop-up pages got counted as site visits, radically inflating overall site traffic counts.

There's no allegation of fraud here; the discussion seems to be centered more along the lines of "who knew this was even possible?" Intriguingly though, it's far from the first time we've all been surprised to learn the way we were counting site traffic was badly skewed.

The first incident I remember is back in the early days of the Internet, when it first became widely known that many ISP's, AOL in particular, were caching web pages. In those days when most everyone had dial-up lines, ISP's could deliver huge performance gains by delivering cached pages from their servers rather than constantly fetching them from destination websites. Result: vast under-counting of site visits.

The second big seismic event I remember is when a programmer casually pointed out at an industry conference that hits and page views were radically different things. Up until that point, hits were thought to be the same as page views, and much of the software of the day was focused on measuring these hits. The problem? A web page with no graphics on it generated a single hit count, but a web page with 10 graphic elements on it generated a hit count of 11. Talk about over-reporting traffic!

Having seen these and a whole host of smaller such "discoveries" over the past ten years, what amazes me -- and to some extent scares me -- is that at this late date, we are still struggling to both define and count traffic. It's all the more remarkable because our industry has so totally bought into the "traffic economy," where your success and even the value of your business is directly linked to the amount of site traffic you can attract.

If traffic is truly our new currency, we are all going to need to work a whole lot harder to stamp out counterfeiting.