There is significant difference between being hacked and being spoofed (a.k.a. cloned) on Facebook. I often see people in a fear spiral when they don’t need to be, and after explaining the difference numerous times it finally occurred to me I could just do a blog post and then share the URL in the future. The spoofers get less of everybody’s time and attention.*
When Spoofing Has Actually Happened
Discovering someone’s been spoofed begins when a friend realizes something’s not right – they’ve received a friend request from someone they’re pretty darned sure they’re already friends with. The person spoofed doesn’t know unless someone tells them because spoofing / cloning is about fooling the friends, not the person being cloned.
When I get a suspicious friend request like this here’s what I do:

