Short answers, pulled from the story.
Bill Weisband was a Ukrainian-American linguist and NKVD agent who worked inside the U.S. Army's Signals Intelligence Service during and after World War II. He is best known for alerting Soviet intelligence that the American Venona Project was on the verge of successfully decoding Soviet communications, causing significant damage to U.S. cryptanalytic operations.
Weisband's NKVD code name was LINK. Three Venona messages also reference a code word ZVENO, the Russian word for link, and Weisband's documented travel dates in July match those described in the ZVENO messages.
According to a February 1948 Soviet internal memorandum, Weisband provided a year's worth of documentary material about American efforts to decipher Soviet ciphers and intercept Soviet communications. The Soviets stated this gave them knowledge of U.S. intelligence on Soviet armed forces, industrial capacity, and atomic energy research, prompting defensive measures that considerably reduced American deciphering capability.
U.S. authorities chose not to bring espionage charges against Weisband because a trial would have required disclosing classified intelligence sources and methods, risking further harm to U.S. intelligence. Instead, he was convicted in November 1950 of contempt of court for failing to appear before a federal grand jury, and sentenced to a year in prison.
Counterintelligence officers did not identify Weisband's role until 1950, after Jones Orin York told the FBI that he had passed secrets to the Soviets and that Weisband had been his handler. By that time, Weisband had already been operating as an agent for years and the damage to the Venona Project had been done.
After serving his sentence for contempt of court, Weisband remained in the United States. He never admitted to being an NKVD agent and lived quietly, working as an insurance salesman. He died suddenly of a heart attack on the 14th of May 1967.