Netcraft will certify web applications that it has tested, showing the date tested, and the number of days spent testing the application. Application testing is very important because even machines that are well administered, and correctly port filtered with no well known vulnerabilities, can be vulnerable to a direct attack on the application’s own functionality.
Whereas automated testing is good at finding common well-known (published) exploits, a consultancy audit can additionally find faults unique to your site, caused by application programming and design errors, as well as more complex configuration errors. A consultancy test can also interpret and exploit leaked information and give constructive advice on solutions.
For more information on web application security testing, see the Web Application Testing page.