Friday, March 27, 2009

Proxomitron, The Universal Web Filter

Proxomitron, the Universal Web Filter, is a filtering web proxy written by Scott R. Lemmon. This program was originally designed to run under Windows 95.

All future development of the program was ceased in 2003 with its author's death; even so, Proxomitron is still viable and used on modern Windows platforms such as XP and Vista.

The program is generally used to block pop-ups and banners, to remove embedded sounds and animation from web pages, to alter or block JavaScript, and to modify the appearance and content of web pages.


Properly configured, Proxomitron intercepts HTTP traffic between the user's browser and web servers. The program is capable of altering web page content by removing or adding text. Additionally, it can add, modify, or delete HTTP message headers, be configured to block connections or redirect requests based on the web page address, and be configured to route connections through a remote proxy. The user can monitor connections and filter activations, if desired.

Program operation is dictated through the use of a configuration file containing specialized filters which can be written, edited, deleted, enabled or disabled by the user via the program's graphical user interface. (Third-party filters can also be imported, or "merged," into the configuration.) The filters utilize a "matching" language similar to the standard regular expressions used in text editing. Additional files, such as "blocklists" and SSL DLLs, can extend filtering capabilities.

Use of the program requires knowledge of the Proxomitron scripting language, as well as some familiarity with at least one of HTTP, HTML, JavaScript, and CSS. The scripting interface was not designed to be user-friendly. Because of these complications, the program can be difficult to customise for novice or non-technical users. A default set of filters is included with the program; advanced filters and filter sets written by experienced users are also available online.


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