Direct mail: Better than Spam?
Another reason why companies want to know not only what Web sites you visit but who you are stems from Internet users' nearly universal distaste for spam, or junk e-mail. Advertisers realize that if they send spam messages to potential customers, they're likely to turn them offââ,¬"permanentlyââ,¬"rather than get a sale.
But many Netizens who abhor spam are nowhere near as resistant to paper junk mail (or direct mail advertising, as it's called in the trade). If a company sees that you're browsing its Web site and it can find out your mailing address, it can send you a snail mail sales pitch, which you may be less likely to reject out of hand.
How they do it
How do sites snoop on your browsing habits and identify you online?
One of the simplest methods is via your IP addressââ,¬"a 32-bit number that serves as your computer's telephone number on the Internet. Whenever your computer sends a packet of information across the Net, it includes its IP address so that the recipient will know where to send a response. If your system has a permanent connection to the Internetââ,¬"for example, via a cable modemââ,¬"its IP address is likely to be constant. So, as you move through the Net, snoops can follow your every step.
Although the IP address is a good way to identify some Web users, it isn't foolproof. Users with dial-up connections to the Internet may get a different IP address each time they call, depending on which of the ISP's phone lines they happen to reach. And all the machines behind a firewallââ,¬"a device designed to keep intruders out of a networkââ,¬"sometimes appear to have the same IP address. (This happens if a mechanism called Network Address Translation, or NAT, is used.)
So, to uniquely identify users and their computers in these situations, Web sites use cookies.
excelant article
one addtional point:
one way to prevent the reading of email in outlook and outlook express from triggering the html bugs, etc is to
1) download your email
2) disable your internet connection
3) read all your email
4) enable your internet connection