An anonymizer is a Web site that proxies your browsing requests (HTTP requests). This means, if you use an anonymizer and you browse from one site to another, to the destination sites it seems as though the site hosting the anonymizer software is communicating with them -- not you. This provides a buffer between you and the destination remote Web server. Some people appreciate this level of protection, because it makes it harder for the remote Web server to gain information about you and your computer, such as your IP address, or data that can be used for identity theft, phishing and pharming attacks. It also provides protection against software on servers from installing adware, installing and reading cookies, and installing Trojan horses or other malicious software.
Be aware, if you use an anonymizer you cannot personalize a Web site, for this takes place through the cookies placed on your system. This means you will need to reenter your personal identification information every time you interact with a site that requires such information.
In my opinion, it is more important to have a properly configured firewall with antivirus and antispyware protection on your local host than worrying about surfing through an anonymizer, but today, the more protection the better.
This was first published in September 2005