Shortly after WikiLeaks released a trove of classified government documents, a small Internet service provider (ISP) got a very serious-looking message from the U.S. government. Law enforcement officials wanted the ISP, Sonic, to turn over information it had about about one of its customers: security researcher and former WikiLeaks spokesperson Jacob Appelbaum.

Headquartered in a sleepy corner of Northern California's wine country, about an hour drive north of San Francisco, Sonic seems like an unlikely candidate to push back against an investigation into one of the biggest information-security breaches in U.S. government history. But that is precisely what the company did....