What every Web site can find out about you

Thought your little visit to www.sexysheep.com was anonymous? Think again. The Internet gives an image of anonymity, but dig a little deeper and you'll find it's a false front.

Almost all Internet sites, and certainly the bigger ones, collect information about their visitors. It's logged by the site server that sends Web pages to your computer, and the data is referred to as Web server logs or weblogs.

You'll be surprised how much information your disloyal computer passes over to the site you're visiting. Nothing as serious as your name or email address, but probably much more than you'd expect.

Here are the main items:

IP address

This is your "street address" for the Internet, it's a string of numbers that identify exactly where you are in the huge ever-changing mass of networks that make up the Internet. It has to be passed to the site so that it knows where to send the pages that you've requested.

The bad news is that your IP address is quite distinctive. It's easy to tell from the numbers which country you're connecting from and which Internet Service Provider you're using.

The good news is that most ISPs use a rolling address system, so you get a different address each time you log on to the Internet (from a range held by your ISP). Though if you're using a computer on an office network it might have its own IP address that never changes.

Ultimately, you can be tracked down from your IP address. Even if it's a rolling address, your ISP keeps records of who is using any address at any given time. In the space of a few seconds they can link any address with a specific user. That's you. But naturally they're reluctant to do it, even for the police.

If you use a free ISP account that didn't need registration, the detail comes from your phone line. These accounts only work with "line recognition", which means the ISP receives your phone number when you log on.

So however you access the Internet, you can be traced. The IP address collected by the site server for its records can be linked directly either to you or to your phone line.

Referring page

Many sites also collect referring page information. Your computer obviously knows where it's just come from, and the shameless electronic traitor freely passes this information on to the next site. "This is the site we arrived from," it says.

Hey, who's in control here?

Browser and operating system

Your computer also tells its electronic friend at the other end what kind of browser you're using, including the version number, and what kind of operating system you have - Windows, Mac, Unix, whatever.

Screen details

Although not all computers do this, many also tell the site server what size screen you have (in pixels, not inches) and what kind of colour resolution you're using - 256, 16 bit, 24 bit. Is there no end to their treachery?

Pages viewed

And finally, without the assistance of your computer, the site server records everywhere you go on the site and how long you stay on each page.

So, just how anonymous was your visit?

And that's ignoring cookies, which tie in your visit to others you've made to the same site before.

Your intimate friend, the network manager

Monitoring by authorities

Email - as private as a postcard