Former Megaupload users took to Twitter and other sites to complain that they'd lost legal material because of the crackdown.

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Story highlights

The U.S. government shut down file-sharing site Megaupload on Thursday

Megaupload let users upload files with a single click

The government says the site's owners knowingly allowed copyright infringement

On Friday, pirated material was still easy to find on other sites

CNN  — 

Megaupload, the file-sharing website shut down Thursday by the U.S. federal government, is a Web hosting tool that now finds itself accused of being an online haven for digital pirates.