Cross Site Scripting via Search Boxes - Warning

[branica]

Matt Cutt wrote this about the dangers of hackers using XSS exploits to gain access to a website. Here is a bit from his post:

If you’ve noticed that your rankings in Google seem to be affected, you might consider a few searches on your site to see if anyone has injected spammy or porn content on your site. If your domain was example.com, you might want to run a few queries such as [site:example.com porn] or [site:example.com biaxin] or [site:example.com viagra] to see whether you run across unexpected results.

[trinitybrown]

Ok what one can do to avoid this problem.