UMG will probably have to argue that MegaUpload is a criminal organisation that distributions disproportionately high infringing content, therefore, them producing essentially an advertisement that tells people about MegaUpload amounts to linking to infringing content. Under this circumstances, DMCA provisions apply because it is a method of circumventing copy protection.

In the end, this is not a battle over free speech. It is a battle by several private interests - YouTube, UMG and MegaUpload over content rights.