SAN FRANCISCO, May 26 — A California appeals court ruled Friday that online reporters are protected by the same confidentiality laws that protect traditional journalists, striking a blow to efforts by Apple Computer to identify people who leaked confidential company data.

The three-judge panel in San Jose overturned a trial court’s ruling last year that to protect its trade secrets, Apple was entitled to know the source of leaked data published online. The appeals court also ruled that a subpoena issued by Apple to obtain electronic communications and materials from an Internet service provider was unenforceable.

In its ruling, the appeals court said online and offline journalists are equally protected under the First Amendment. “We can think of no workable test or principle that would distinguish ‘legitimate’ from ‘illegitimate’ news,” the opinion states. “Any attempt by courts to draw such a distinction would imperil a fundamental purpose of the First Amendment.”

The ruling states that Web sites are covered by California’s shield law protecting the confidentiality of journalists’ sources.

Apple had argued that Web sites publishing reports about Apple were not engaged in legitimate news gathering but rather were misappropriating trade secrets and violating copyrights. But in its ruling on Friday, the panel disagreed.

“Beyond casting aspersions on the legitimacy of petitioners’ enterprise, Apple offers no cogent reason to conclude that they fall outside the shield law’s protection,” the ruling states.

If upheld, the ruling could have far-reaching impact in California courts on other writers who publish electronically, including bloggers who regularly publish news and opinion online without the backing of a mainstream news operation.

“This ruling will probably prove instructive to other online writers,” said Kurt Opsahl, a lawyer with the Electronic Frontier Foundation, a civil liberties organization, who argued the case in front of the appeals court last month. “It says that what makes a journalist is not the format but the function.”

Apple declined to comment Friday on the ruling or on a possible appeal.

Apple’s close guarding of company secrets, particularly unannounced products, is legendary. Friday’s ruling arose from a suit filed in December 2004 against the unknown individuals who Apple said had leaked information about unannounced Apple products to two sites devoted to news of the company, AppleInsider and PowerPage.org.

Both sites published reports in November 2004 describing secret Apple projects, including one known at Apple by the code name Asteroid.

Apple did not sue the sites directly but sought to subpoena their e-mail records. As part of the investigation, Apple subpoenaed the e-mail records of Nfox, the company that provided Internet service to Jason D. O’Grady, the publisher of PowerPage.

About the same time, Apple filed a trade-secret suit against Think Secret, another online news site that the company accused of publishing confidential data about its future products. That case is pending.

Friday’s ruling is also significant because it addresses whether private e-mail is protected from subpoenas. “The court correctly found that under federal law, civil litigants can’t subpoena your stored e-mail from your service,” said Kevin Bankston, a lawyer for the Electronic Frontier Foundation.