The discussion so far has been mostly on what an "ordinary" site can tell about people who visit. For the most part, the information you leave in your wake is fairly trivial. The typical cookie probably can contain information that could be "extracted" by a malicious site that most people would consider "invasive," but it requires malicious intent for a site to read other sites' cookies.

The "AdAware" program that has been mentioned in several similar threads purports to "clean your machine" of certain "nosy" cookies that are purported to allow businesses to track "surfing habits" of individual users; although it is not clear whether these cookies identify you (when used as they're supposed to be), or whether they merely say that some particular individual looked at some sites that may be related

The contention is that these "spy" cookies (doubleclick is a prime example) keep track, in the cookie, of all sites you visit, so that (for example) a "doubleclick site" can tell where you've been recently.

I haven't made any serious investigation of what's in a "doubleclick" cookie, and I suspect that it's nothing "too personal," but I do take offense to their assumption that they have a right to follow me around without asking my permission. This should be called "stalking" in any criminal court in the country, IMHO.

There is a third "level" of true "spyware," which can record "very personal information," down to "screen shots" of what you look at and individual keystrokes that you type. These programs generally require deliberate installation on your machine, and in theory are used "only by persons like network administrators with a legitimate right to track your activities - or parents who want to keep track of their childrens' surfing." (Wanna buy some lakefront property in Arizona?)

An article in the July 2002 PC Magaxine, titled "Look Out: Under surveillance or undercover, you need to know ..." that gives some information on legal? programs of this kind. I haven't looked, but the article should be up at www.pcmag.com. (No link because this is a rather "messy" site, and you do need to sign in and give them an email addy to be able to get around on the site. I consider them "trustworthy - at arms length," and there is good info there.)

John