When you surf the web, you are bound to see banners. So what, you've gotten used to the banners and you might even click on some once in a while, but have you ever wondered how banner systems work?
Have you noticed that in the past few years banners became more appealing?
Do you notice something is different when you surf the web from a different computer?
First, take a deep breath and relax. This is not paranoia.
Banner systems have evolved from linked images to graphical, interactive presentations, which seem to know what you want. The experienced among you are probably thinking by now, that this write-up is going to be about cookies. It is not.
When you enter a modern dynamic website, it will call upon the banner system to present you with a banner. The banner system will then attempt to collect as much information about you, within the fraction of a second it has, and output you with the most appropriate advertising. Keep in mind that modern banners can be images, plain text, html code, flash animations, java presentations or anything else, as long as the user supports it.
The banner system will determine which banner to output, after excluding all inappropriate banners. There are two sets of conditions which exclude banners from the banner pool: the server side conditions set, and the set which is based on the information the banner system gather about the user.
The server side set of conditions will attempt to exclude banners according to the following:
- Manual setting of the banner availability - a banner can be turned on or off.
- The page from which it is requested - you might want to restrict certain banners to certain pages.
- The current timeframe - you might want to restrict a banner to be only shown on certain days, at certain hours.
- Limitation on views - a limitation can be set on the number of times a banner may be shown, this may be set to a certain amount of time, or indefinitely (i.e. after showing the banner 1,000,000 times, do not show it again).
- Limitation on clicks - same as with views only applied to the number of times the banner was clicked.
And these are just a few because, when it comes to conditions, only your imagination sets the limits. There is also the set of conditions based on the information the system gathered from the user. These are usually, but certainly not always, limited to:
- The country from which you log in (accomplished by resolving your ip address).
- The web browser you use, including the version.
- Your operating system, also including the version and the language it is set to.
- The previous page you have accessed, either within that same website or prior to entering it.
This is it, by forming a structure of conditions and setting the most important conditions first, the system can exclude all inappropriate banners and remain with the perfect advertisement to output. The banner system starts off with a big number of banners and excludes those which don't meet the required conditions. This will repeat until one banner is left or until you run out of conditions. The system will then present the one banner it has left with, or pick a random banner from those which have passed all the set conditions (some banners can have more chances of being selected than others at this point, if the system supports it).
So what's the big deal with cookies you might ask?
Well, cookies are used to store small strings of information on the user's system, this can be used to identify the user and track him, but only within the domain which set that particular cookie. The problem begins when different websites all use the same big banner system, developed by some advertising company. This banner system works from it's own domain and thus the cookie it sets is available to it from any website which runs it's banner system. The advertising company which built the banner system can then form an agreement with the websites which are using it, to share sensitive information.
So let's say you purchase a horror movie in some e-store, and that store shares your gender and age with the advertising company. Voila! From now, all the banners of that advertising company will be specific for your age and gender.
And what if you happen to click on a banner which invites you to join a homosexuals support group? God only knows what banners you are going to see from now on...
"Not that there is anything wrong with that." -- Seinfeld | 
