The Red Scare refers to two periods of intense anti-communist sentiment in the United States in the 20th century. During World War I and again in the late 1940s through 1950s, there was widespread fear of communist infiltration of the US government. This led to investigations and persecution of suspected communists, such as Ethel and Julius Rosenberg who were executed for espionage, and Alger Hiss who was accused of being a communist spy. The government implemented loyalty programs and acts restricting immigration to crack down on communist threats during the Cold War era.