I think there may be some confusion about what information is readily available for others to see when you browse the Internet. So I have created a page that will show you what can typically be seen - When You're on the Internet. Click here, and then you can come back and read the rest of the article.

1. One of the urban legends seems to be that 'they' know where you live - 'they' don't!
They can see your Remote IP Address, and with that they can get geolocation information. Geolocation information is public information about the owner of that IP address, which is usually your ISP provider, i.e. Comcast, PacBell, Verizon, etc. Within the U.S. it is easy to resolve the State, but as you try to get more fine grain resolution, the ability to accurately determine the County, or City is not very likely, as the best resolution is probably about 25 miles. A humorous example is that Facebook is always showing me ad's of attractive young women that want to meet me and live in (my_city).

2. Useful information 'they' do know about your monitor, browser, OS and plug-ins.
• Monitor H and W dimensions in pixels, and screen resolution in bits
As more people have 'smart devices' the ability to detect the screen size/resolution is critical in optimizing the image/video they receive.
• Browser make and version
In the early days when there were only two browsers (Netscape and Internet Explorer) there were significant differences between the two, and much code was written to detect each browser and provide pages unique to that browser. Now, there are many browsers to choose from, and thankfully, they are more similar than different. Accurately detecting the browser (browser sniffing) is sometimes difficult as there was not a rigid standard, but more of a suggested guideline.
• OS is usually Microsoft, Apple, or Linux
Again, there may be times when knowing the OS allows you to customize content
• Plug-ins (and Javascript or cookies)
Once again, a lot of legacy reasons for this. In earlier times, not everyone had Javascript enabled, and without it many features could not be provided. Same with 'cookies', and now most websites won't allow you to enter without 'Cookies Enabled'.

The mention of 'cookies' provides a perfect segue to explaining what 'they' are capable of collecting, depending on your habits. It is possible for multiple websites to aggregate 'raw data' (visits, cookies, etc.) and make assumptions about an individual.
EXAMPLE: If someone from a specific IP address shopped for cosmetics and dresses, they might assume the gender is female and serve pages to that IP Address that reflect those interests; even identifying relevant stores in their local area.

If you fill-out a lot of 'form' information on websites, it is possible that much more specific information could be shared among multiple websites, which provides a more detailed profile, and identifies you personally.

Practice Safe Surfing habits, and reduce the likelihood of identity theft, or financial loss.