A New York Times reporter need not testify in court about who gave him details on a top-secret CIA program targeting Iran, a federal judge has ruled.

In May, federal prosecutors subpoenaed Times reporter James Risen to testify against former CIA officer Jeffrey Sterling, who's accused of revealing top-secret details about a CIA effort to undermine Iran's nuclear program. Prosecutors allege that Sterling was a source for Risen, who published details about the CIA operation in his 2006 book, "State of War."