Dozens of free tools combat phishing and other Web scams, many in the form of browser extensions that warn users when browsing a phishing site. Carnegie Mellon researchers tested the effectiveness of 10 of these anti-phishing toolbars.
Source: Phinding Phish: An Evaluation of Anti-Phishing Toolbars, Lorrie Cranor, Serge Egelman, Jason Hong, and Yue Zhang, Carnegie Mellon University, Pittsburgh, Penn., November 2006.