While everyone's skeptical about how and why so many tech companies are involved with PRISM, the New York Times has run a heartening piece which describes how Yahoo fought hard—but ultimately failed—to avoid joining the initiative.
A document dating back to 2008 shows that a company now identified to be Yahoo petitioned the secret Foreign Intelligence Surveillance Court (FISC) to review an order from the government. Yahoo believed that its contents violated the Fourth Amendment; the FISC dismissed Yahoo's concerns as "overblown".
FISC apparently claimed that it was "settled beyond peradventure that incidental collections occurring as a result of constitutionally permissible acquisitions do not render those acquisitions unlawful." Claiming that Yahoo "presented no evidence of actual harm," the company's concerns were tossed aside.
So when Yahoo recently claimed to have "not joined any program in which we volunteer to share user data with the U.S. government", it was telling the truth. It has no option but to comply—despite making the best efforts it could. [New York Times via Verge]