Fear, such as will constitute extortion, may be induced by a threat, either:
1. To do an unlawful injury to the person or property of the individual threatened or of a third person; or,
2. To accuse the individual threatened, or any relative of his, or member of his family, of any crime; or,
3. To expose, or to impute to him or them any deformity, disgrace or crime; or,
4. To expose any secret affecting him or them.