Technical
Check installed filters
To check which filters that are active on a SQL Server, one of the following commands could be executed:
EXEC sp_help_fulltext_system_components 'filter';
SELECT * FROM sys.fulltext_document_types;
You can also install more iFilters. See section Install new iFilters
Detailed information of full-text search
A good walk-through of how full-text search works can be found here.