XDCCXDCC refers to IRC bots running file sharing programs. XDCC bots serve one or more usually large files for download using the DCC protocol. Its use is widely understood to be a protocol extension by which illegal content, usually MP3s or warez, can be listed and, subsequently, downloaded.
Frequently, warez groups utilize connections with fast upstream speeds in order to mass distribute their releases (usually ISOs compressed in either RAR or TAR format). XDCC is quickly gaining popularity over older methods of computer piracy such as newsgroups and fserve. Unlike peer-to-peer transfers, XDCC is often hosted on connections with massive upstream bandwidth, the most popular dumps (server computer with pirated software) are usually connected to 100MBit or EDUs.