It’s official: Indymedia is under investigation by the Secret Service, after several posts revealing private information of Republican Convention delegates.

WASHINGTON - The Secret Service is investigating the posting on the Internet of names and personal information about thousands of delegates to the Republication National Convention 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 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.