Privacy wasn’t a concern for her until it was too late.

The woman, who agreed to share her story if she weren’t to be identified, told me she left home one midnight, after four years in a relationship. She moved away and restarted her life. But then, she says, she was bombarded by phone calls from men soliciting her for sex. Then came bizarre friend requests on social media. She says one man showed up at her house.

She...