A federal judge ordered Verizon to provide the Recording Industry Association of America with the identities of customers suspected of making available hundreds of copyrighted songs.
Car hire companies have been asked to forward details to police of customers suspected of using vehicles for criminal purposes, in the wake of last week's terror attack.
After years of negotiations with Hollywood and the music industry, the nation's top Internet providers have agreed to a systematic approach to identifying customers suspected of digital copyright infringement and then alerting them via e-mail or other means.
Last month, the United States Justice Department won an agreement with UBS, the Swiss banking giant, in which it agreed to turn over the names of about 250 customers suspected of avoiding American taxes.
But the three-judge panel of the United States Court of Appeals for the District of Columbia also had tough questions for Verizon, which is challenging the record industry's interpretation of a 1998 law that allows copyright holders to force Internet service providers to identify customers suspected of copyright infringement.
TalkTalk, with more than 4 million UK internet users, said that "many draconian proposals remain" in the bill, including some that would allow content companies to force internet service providers (ISPs) to block the connections of customers suspected of online copyright infringement.
O2 customers suspected of illegally sharing pornographic films made by Ben Dover Productions will begin receiving letters from the film-maker shortly.
The firm said the occasional letters alleging dishonesty had been sent more than 18 months ago to a few customers suspected of fraud but had not been used since.
According to the BBC quoting The Times, broadband firms which failed to enforce the rules could be prosecuted, and the details of customers suspected of making illegal downloads would be made available to the courts.
Their quarry: customers suspected of illegally parking in spots reserved for the disabled.
