The warning came after a June 28, incident in which a women let two men into her home after they said they were selling newspapers, the San Francisco Chronicle reported Saturday.

The men are said to be in their 20s and have dark hair, the newspaper said.

Police said one of the men allegedly showed his genitals to the woman after they had a brief conversation, while the other fled.

Officials said Berkeley residents should be extremely cautious when answering the door for people they don't know.