5 signs your ASP.NET application may be vulnerable to HTML injection
If you don’t encode data when using any of the following methods to output to HTML your application could be compromised by unexpected HTML turning up in the page and modifying everything from formatting though to capturing and interfering with form data via remote scripts (XSS). Such vulnerabilities are incredibly dangerous.
Using MonoRail or Microsoft’s MVC does not make you automatically immune — use {! }
{! } in MonoRail’s Brail engine and the HtmlHelpers in Microsoft’s MVC to ensure correct encoding.