The security set commands are used for configuring specific DCC validation and filtering settings on your server.
DISABLE - Disable all DCC filters.
ENABLE - Enable the DCC filter and validation system..
FILELIST - Configure the files to filter.
LIST - List DCC settings.
SET - Specific DCC Settings.
/as help security dcc <topic>
DCC filtering is very nice for your community members as it will protect them from many (not all) of the dangerous scripts and viruses that can be sent from one user to another. If you're using a java/html/wap system and aren't allowing IRC clients then you do not need to enable these settings.