OMG KINDA SCARY

so, my sis was on facebook and she got a friend request from some dude named Mohamed Riswan. What the heck! we dont know anyone named mohamed. I know that people friend random strangers, which is dangerous,but how did they even come across her facebook?!?!?! its not like they have any mutual friends!!! if you have a solution, i wana hear it! so creepy! :(