Speaking in a live Facebook Q & A, she said: "There was a website set up that was threatening to release naked images of me, with like a countdown and whatever else.
"I knew it was a hoax. I knew the pictures didn't exist."
Recently, Emma Watson also received threats within hours of making her speech at the United Nations.
The 'Harry Potter' star launched the HeForShe campaign, which aims to promote gender equality, at the UN in September but has revealed the threats left her family incredibly shocked.
She said: "A lot of people close to me knew gender equality was an issue but didn't think it was that urgent. You know, 'We live in Great Britain - this is a thing of the past. We're fine. We're good. We have got far enough.'
"When they saw that the minute I stepped up and talked about women's rights I was immediately threatened. I mean within less than 12 hours I was receiving threats.
"I think they were really shocked and one of my brothers in particular was very upset."
See the gallery below for more images of the stunning Emma Watson