Security researcher Prakhar Prasad disclosed an XSS vulnerability in the Offensive Security website.
Offensive Security are the creators of the BackTrack and Kali security linux distributions and offer security training and certifications, including web security training where you can learn to find similar XSS bugs:
"From mind-bending XSS attacks, to exploiting race conditions, to advanced SQL injection attacks, Advanced Web Attacks and Exploitation will broaden your knowledge of web application hacking and help you identify and circumvent various protection mechanisms in use on the web today."