Social media and emails are the worst culprits for spreading virus email messages. Most computer users who are even a little savvy delete these and go on, but for some people -- especially elderly users -- these messages can be frightening.
These hoaxes, like most hoaxes, prey on the lack of knowledge most people have about how computers work. I had a boss who used to freak out every time she got an email about a virus. She would place a frantic call to our IT guy, who would tell her it was a hoax and to hit the delete button. She knew nothing about computers, so she was a perfect target.