SAN FRANCISCO — A federal judge on Thursday ruled that Twitter, the popular microblogging platform, must reveal information about three of its account holders who are under investigation for their possible links to the WikiLeaks whistle-blower site.

The case has become a flash point for online privacy and speech, in part because the Justice Department sought the information without a search warrant last year. Instead, on the basis of a 1994 law called the Stored Communications Act, the government demanded that Twitter provide the Internet protocol addresses of three of its users, among other things. An Internet protocol address identifies and gives the location of a computer used to log onto the Internet.

The three people came to the Justice Department’s attention because it believed they were associated with WikiLeaks.

Twitter informed the three people — Jacob Appelbaum, an American computer security expert, along with Rop Gonggrijp, a Dutch citizen, and Birgitta Jonsdottir, a member of Iceland’s Parliament — of the government’s demand for information earlier this year.