HDCP stands for High-bandwidth Digital Content Protection. According to Wikipedia, "HDCP does not allow copying permitted by fair use laws. The system is meant to stop HDCP-encrypted content from being played on devices that do not support HDCP or which have been modified to copy HDCP content."
HDCP has been cracked and the decryption software has been released as open source software.
"We have released an open-source (BSD licensed) implementation of the HDCP encryption/decryption algorithms. The code includes the block cipher, stream cipher, and hashing algorithms necessary to perform an HDCP handshake and to encrypt or decrypt video," software engineer Rob Johnson said.