The Secret Service is investigating the posting on the Internet of names and personal information about thousands of delegates to the Republication National Convention (search) in New York, officials said Monday.

The probe focuses on anonymous postings on a Web site operated by the Independent Media Center, which describes itself as "a network of collectively run media outlets for the creation of radical, accurate and passionate tellings of the truth."

The American Civil Liberties (search) Union, whose lawyers are representing the Web site's administrators, gave the Secret Service the e-mail addresses of the administrators in a letter Monday. But the ACLU pointed out that they are not responsible for postings of lists of GOP delegates because the site guarantees anonymity to anyone who wants it.

"This type of investigation is really a form of intimidation and a message to activists that they will pay a price for speaking out," said Ann Beeson, the ACLU's associate legal counsel. "The posting of publicly available information about people who are in the news should not trigger an investigation."

Secret Service officials would not comment beyond confirming that the investigation was continuing. But federal law enforcement officials, speaking on condition of anonymity because the probe is active, said there were concerns that posting of the delegate lists could subject the delegates to harassment, acts of violence or identity theft.

There are several lists of Republican National Convention delegates posted on the Indymedia site, including one listing more than 2,000 of them. Included are names, home addresses, e-mail addresses and the New York-area hotels where many are staying.

"The delegates should know not only what people think of the platform they will ratify, but that they are not welcome in New York City," said one posting, first reported Monday by The New York Times.

A federal grand jury in New York has subpoenaed a Web hosting service, Calyx Internet Access, for Indymedia contact information. Calyx President Nicholas Merrill said he refused initially to voluntarily give the information to the Secret Service, asking instead for the subpoena to protect clients' privacy. Calyx is also being representing legally by the ACLU.