Cross-site-scripting?

Hey guys,

So a couple of people and myself have a blog that revolves around new media technologies, that started off as a school project and has since been going on. We allow people to contribute to comments and occasionally to post, the goal being to create a rich user-generated content experience. Recently we started observing links in comment boxes that redirected our readers to undesirable content and mostly spam. This has been happening increasingly, and after some research we found that it could be the result of cross-site-scripting (hackers inserting malicious script in content). Is there a way to stop or protect our blog from these attacks?

Many thanks!