Megaupload boss Kim Dotcom on Thursday accused US authorities of mounting a "misleading and malicious" case against him, saying there was no way they could win a landmark online piracy action.

Free on bail in New Zealand after winning a legal fight with prosecutors who wanted keep him behind bars after his January 20 arrest, a defiant Dotcom was confident of beating charges brought by the US Justice Department and FBI.

"For every email in their indictment, I have 100 others that disprove it," Dotcom told the New Zealand Herald in his first interview since being released last week after a month in custody.

The US indictment alleges Megaupload and related file-sharing sites netted more than $175 million in criminal proceeds and cost copyright owners more than $500 million by offering pirated copies of movies, TV shows and other content.

But Dotcom said the charges ignored evidence he personally attempted to stop copyright infringers from linking to Megaupload and his business employed a 20-strong team dedicated to taking down material which may have been copyright.

"How do you cherry-pick in a way that is so misleading and malicious?" he said. "For me, sitting in my cell, I'm thinking, 'Why are they doing this, they can't win?'"

The German national predicted it could take years to prove his innocence in court. His fight to be granted bail was only an initial skirmish, with a battle looming in New Zealand in August when US authorities will seek his extradition.

If the 38-year-old is transferred to the United States, a lengthy court case appears inevitable as authorities pursue the largest Internet copyright piracy case in US history.

Prosecutors have vowed to seek maximum penalties of 20 years on racketeering and money-laundering charges if Dotcom, who legally changed his name from Kim Schmitz, is brought before a US court.

Dotcom said he was stunned to be locked up after New Zealand police, cooperating with the US investigation, raided his sprawling Auckland mansion on January 20.

He complained of his treatment during his first night in custody, telling the newspaper: "Every two hours they would wake me up, 'I said this is torture, this is sleep deprivation.'"

The portly millionaire said that if there was a bright side to his incarceration, it was the 16 kilograms (35 pounds) he lost while behind bars.

Despite his legal woes, Dotcom said he wanted to remain in New Zealand for the long term with his three children and wife Mona, who is pregnant with twins.

"This is the country where I want to live and where I want my children to grow up, I love it here," said the businessman, who moved to Auckland in early 2010.