Evaluate SQL injections, XSS holes, and site security.
Hackbar is a simple security audit / penetration test tool. This toolbar will help you in testing SQL injections, XSS holes, and site security. It is not a tool for executing standard exploits and it will not teach you how to hack a site. Its main purpose is to help a developer do security audits on his code.
If you know what you are doing, this toolbar will help you do it faster. If you want to learn to find security holes, you can also use this toolbar, but you will probably also need a book, and a lot of Google.