Anonymous surfing

A surprising amount of information about you can be gathered as you surf the Web - including the kind of computer and operating system you use, the sites you've visited recently, your location, and possibly your company. This comes about in several ways. For instance, when you are on the internet, your computer is allocated a unique numerical address called an IP address. Records of this are kept by your internet service provider, and can be accessed by people wanting the information. Some less scrupulous people sell lists of these. Another way is for the web page to plant a "cookie" in your computer, which it can then track. Most cookies are fairly benign - for instance, it tells a site whether you have visited before, and saves you having to provide a password every time you visit.
There are various ways to keep your surfing information private. One is to use what is called a proxy server, essentially an internet site that you log on to, which then disguises your computer's IP address, so it can't be traced. Another is to use programs like Tor, which is a free program that takes all of your Internet communications and sends them around a large network of "onion" routers that make it impossible for sites or people to invade your privacy. There's lots more info on this at the Tor site.