Elizabeth Bentley

The so-called "Red Spy Queen," Bentley, a self-confessed former courier for Russian agents, testified before HUAC on July 31, 1948 that Assistant Treasury Secretary Harry Dexter White and 31 other government employees were spies. Bentley told the FBI that she heard through a secondhand source that there was a spy in the State Department, but she did not name Alger Hiss, and she did not testify at his trials. Although the truth of her allegations remains under investigation, not one of the 32 people she named was convicted of espionage. 

See the entry on William Remington for more on the impact of her testimony.