Many large companies and online service providers--notably America Online--use proxy servers within their networks to reduce congestion. When one user visits a Web page, the images and other files are copied onto the proxy server in a so-called cache. When subsequent visitors within that organization visit the same Web page, the files are served from the proxy's cache instead of across the entire network again.
Cacheing has been a bugaboo because it prevents Internet publishers and marketers from knowing exactly how many people are visiting their sites. Some estimate as much as 25% to 40% of all ad impressions are uncounted due to caches, although others say those figures are blind guesses.
For more on this story, see the full article in Interactive.
Copyright April 1997, Crain Communications Inc.