I'm going to use an analogy to explain my thoughts on this subject.
Suppose you're shopping in a mall. In your wallet, you might have some cards issued by stores that give you discounts or special services to people who carry those cards. So you might have a Gap card, or a Best Buy Rewards card, or a card from a shoe store that gives you a bonus after spending a certain amount in their store. You probably have cards or keychain tags from supermarkets that give special discounts for shoppers as well.
So far, so good. You got all of these cards voluntarily, in an agreement with the merchant that you would get something in return for patronizing their store and letting them track your purchases.
Now suppose that you go into a store and someone at the door hands you a card and asks you to carry a card with you so that they can track what you look at in the store. What will you get in return? Nothing. Just carry the card while you're in the store. Okay, so you go along with this.
When you leave the store, you try to give the card back to the guy at the door who first gave it to you. No dice. You have to keep the card and carry it with you. The next time you enter the store, the guy at the door asks to see your card and, again, when you leave, you have to take it with you. To make things worse, every store you visit now hands you a card and, by the time you leave the mall, your pockets are bulging with these useless things that have no benefit for you.
Welcome to the world of web browser "cookies." A cookie is a piece of data that a web site puts on your computer so that it can read the information back at a later date. Originally, cookies were developed to aid in creating web commerce sites, and to give certain benefits to the site's visitors.
The problem originates because every time you get a web page, it's a whole new world for the web server -- they don't know who you are from page to page. By putting a piece of data on your computer, they can identify you uniquely, as opposed to another member of your family on their computer which uses the same router as yours.
Cookies allowed web sites to have shopping carts, where you go from page to page, adding new items as you go. The site tracks you and your purchases by putting cookies on your computer. When you go to checkout, all of your purchases in your shopping are ready to be totaled and paid for. Cookies let you log on to a web site and stay logged on as you go from page to page. Cookies can save your user ID for a web site, so you don't have to remember it. And cookies can remember your preferences for a web site.
I don't mind the beneficial cookies, since I asked for them to be there. The tracking cookies, on the other hand represent an invasion of privacy that makes me think of George Bush's warrantless wiretapping program that spies on American citizens. Tracking cookies, placed on your computer without your knowledge or your consent, are definitely "spyware."
There are two reasons why web sites use tracking cookies. The first is ego. I wanna see how many people are reading my blog. Don't you? And it's made even worse since Google and others offer some form of this service for free. Now, almost every web site you visit puts some sort of tracking cookies on your computer.
The second reason for tracking cookies is, of course, money. By showing significant web traffic a site can sell advertising, just like a newspaper or magazine with their circulation figures.
There are some technical problems with tracking cookies. Most involve the fact that a web site has to call the statistics web site while sending you a web page so the data can be recorded there. This adds an additional delay that slows the original site down. If the statistics web site is down, or slow, or if their part of the network is slow, the original web site could time out and fail. And believe me, this does happen. You can identify this when a page starts to load in your browser and then takes a mysterious time out.
I've experimented with a number of browser "add-ons" that are meant to control the cookie problem, but none seem to have the ability to separate the tracking cookies from the beneficial cookies.
In the future, I imagine that someone will find the answer to this problem and at that time all of the people using browser cookies solely to track their web site's visitors will suddenly get a rude surprise.