A man secretly recorded a woman performing an intimate solo sex act on camera and then sent the video to her daughter ... at least according to a new lawsuit.

A California woman named Crystal Merrill is suing a Nevada man named Frank Harris, claiming they were having cybersex over Facebook Messenger in 2022 when he secretly recorded her without her knowledge or consent.

Crystal claims Frank ultimately sent the intimate visuals to her daughter via text message and email in 2023 ... and she says he then contacted her and threatened to upload the footage to Instagram, Pornhub, Facebook and TikTok.

She says she didn't consent to Frank recording or sharing the video -- with her daughter or anyone else for that matter -- and she's going after him for at least $150,000 in damages and other relief.