A Java-based web proxy for assessing web application vulnerability. It supports editing/viewing HTTP/HTTPS messages on-the-fly to change items such as cookies and form fields. It includes a web traffic recorder, web spider, hash calculator, and a scanner for testing common web application attacks such as SQL injection and cross-site scripting.
For downloads and more information,
visit the Paros proxy homepage.
Not too surprisingly I have to agree with Rui.
OWASP ZAP is a fork of Paros, has significantly extended it and is very actively maintained.
Its free, open source and theres no 'Pro' version.
Its also a community project, so anyone can easily contribute.
Paros Proxy is old, as in 2005 old, as in java 1.4.2 old. difficult to get it to install on anything recent. Try instead the OWASP Zed Attack Proxy (ZAP), which is a fork of Paros Proxy, runs on current systems, and is constantly updated (current version is 1.3.3 from October 2nd this year, 2011). See https://www.owasp.org/index.php/OWASP_Zed_Attack_Proxy_Project
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