To understand how one "unlocks" a site like Extratorrent, one must first understand how it is locked. The restrictions placed on torrent sites generally fall into two categories: ISP-level blocks and domain seizure.
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If you're looking for academic or technical analyses on the subject, there are papers and articles discussing the implications of torrenting, the arms race between torrent sites and authorities, and the socio-economic impacts of file-sharing. These can often be found on academic databases like Google Scholar (scholar.google.com). To understand how one "unlocks" a site like