More than three years have passed since Canadian police seized 32 Megaupload servers on behalf of U.S. authorities seeking to prosecute company founder Kim Dotcom in one of the world's largest copyright infringement cases.

Still, no one — except perhaps officials with the file-sharing company itself — knows what's on the servers. 

At issue now is how much of this seized Canadian data can be shared with the U.S. Department of Justice, which is very eager to press its case against Dotcom, who is currently fighting extradition from New Zealand, where he's a permanent resident. 

In a Toronto court on Monday, Crown attorney Moiz Rahman, acting on behalf of the U.S., recommended bringing in a U.S. "clean team" — an American term for a group of forensic investigators independent of the case — to sift through the 25 terabytes of data on the servers to pick out relevant files and separate them from personal information. 

But Megaupload's lawyer argued that the Ontario court can only ask the U.S. police officials on the so-called clean team to "double pinky promise" that they won't share information not relevant to the case, since there's no way to enforce the court's decision south of the border.

"Once they return to the United States, that's nothing more than a promise," said Scott Hutchison.

U.S. regulators shut down Megaupload, founded by the notorious Kim Dotcom, in January 2012. At the time, it was one of the world's largest file-sharing sites. (Dotcom, a German-Finnish entrepreneur who was born Kim Schmitz, changed his name in 2005.)

Dotcom and others face charges related to copyright infringement, racketeering and money laundering. Prosecutors argue the company essentially rewarded users for uploading popular content such as stolen movies and TV shows.

The three-year-old case has been mired in complications and delays, including here in Canada.

On Jan. 18, 2012, an Ontario judge granted a search warrant to seize 32 servers in Canada — equivalent to the amount of data stored on 100 laptops, according to Megaupload lawyers.

A year later, a different Ontario judge rejected a request to send mirror copies of what was on those servers to the U.S, saying such a request might be overly broad.

Instead, the justice ordered both parties to find a way to filter out and share only the relevant data.

The "vast majority" of the data, argues Megaupload lawyer Hutchison, is likely everyday files uploaded by innocent users of the file-sharing service, which allowed users to upload and share large files such as photos, videos and documents.

"We don't know what we're turning this clean team loose on," said Hutchison at Monday's motion hearing.

'Very minor' information

Even if the court assumed half of Megaupload's daily users — estimated to be 50 million at the time of the site's shutdown — were innocent, that's a lot of irrelevant files in the hands of U.S. officials, he said.

Instead, Hutchison proposed that an independent Canadian examiner be hired to review the content.

Crown attorney Rahman argued that having a U.S. clean team do the sorting posed no greater risk than the practice of allowing U.S. police to come into the country to witness evidence.

He says the clean team would review the materials without delving too deeply. It would then present an index of what's contained on the servers to the court, which would decide what gets turned over to the U.S.

Rahman noted that the treaty guiding U.S.-Canada information exchange allows for the Ontario court to place restrictions on how the evidence is used. 

"That's a little bit of cold comfort to me," said Justice Michael Quigley.

Beyond that, Rahman said this data pales in comparison to other information shared easily with the U.S., such as wiretaps.

"What's being proposed here looks very, very minor in terms of what we're exposing foreign officials to," said Rahman.

Ultimately, however, the issue comes down to cost. Rahman said the price tag to hire an independent Canadian examiner would be "prohibitive."

The judge ordered both parties to do a cost comparison between the U.S. clean team versus. hiring Canadian experts before a decision will be made.

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