XSS is popular technique that gained a lot of interest since last three years. I think that this technique uses vulnerabilities that are know for much longer than 3 years, but now it has it’s own 5 minutes 🙂 To learn something more about it and ways to prevent from it I’d selected few articles. I hope they’ll give you more insight view in the matter.
Preventing XSS on your site:
and practical ones: