Microsoft has released an open-source Web Protection Library (WPL) to help developers protect web sites from cross-site scripting attacks. The WPL is being offered as part of a defense in depth strategy to add an extra layer to any validation or secure coding practices. It essentially provides a list of encoding functions for user input, including HTML, HTML attributes, XML, CSS and JavaScript. AntiXSS differs from the standard.NET framework encoding by using a white list approach. All characters not on the white list will be encoded using the correct rules for the encoding type.
Source: https://threatpost.com/microsoft-releases-anti-xss-web-protection-library-060210/74047/