have no access to the files, which they say would strip them from any possible liability for knowingly enabling users to distribute copyright-infringing content, which Washington says is illegal.
"Even if we wanted to, we can't go into your file and snoop and see what you have in there," the burly Dotcom said.
Dotcom - a German national who also goes by the name Kim Schmitz - and his colleagues face years in prison if they are convicted, although the case is expected to drag on for years.
Known as much for his previous cyber crime-related arrests as his penchant for fast cars and yacht parties, Dotcom promised an extravagant launch for Mega as builders put the finishing to a festival-sized concert stage in the mansion's grounds.
Two helicopters circled overhead as workers erected a massive white replica of Mega's capitalised, block-lettered logo on the hills flanking the approach to the mansion. Dotcom was coy about what guests could expect from the event.
Expecting huge interest in its first month of operation, he said Mega's launch will be a far cry from when Megaupload went live in 2005.
Then, he and his colleagues were glued to their computer screens in a tiny office, cheering each time the counter showing the number of hits on the site ticked up towards 10.
"I would be surprised if we had less than 1 million users," Dotcom said.