A federal judge upheld an order requiring The New York Times to disclose a columnist's confidential sources as part of a libel lawsuit filed over its coverage of the 2001 anthrax attacks.

Former Army scientist Steven Hatfill sued the Times, arguing that a series of articles by columnist Nicholas Kristof falsely implicated him in the anthrax mailings that killed five people in late 2001.

U.S. Magistrate Judge Liam O'Grady in October ordered the newspaper to disclose the identities of three of Kristof's sources. The judge said Hatfill's right to move forward with his lawsuit outweighed the limited immunity Virginia gives reporters from disclosing sources.

U.S. District Judge Claude M. Hilton upheld that ruling Tuesday after the Times appealed.

Hatfill's lawyers want to question the sources to determine if Kristof's reporting was accurate. The Times had cited FBI sources in reporting Hatfill was one of a limited number of people with the access and technical expertise to manufacture the anthrax and that he failed lie-detector tests.

Hatfill was a physician and bioterrorism expert who worked at the Army's infectious disease laboratory at Fort Detrick, Md., in the late 1990s.

The Justice Department has refused to discuss Hatfill but recently said the strain of anthrax used in the attacks was accessible to more people than initially reported. No one has been charged in the attacks.

In Friday's newspaper, George Freeman, vice president and assistant general counsel for the Times, called the ruling disappointing but added: "We are confident that in the end, the columns will be vindicated."