I've never read about them attacking people, but they will go after small pets and rummage through your trashcan. The biggest danger to humans is having one fall on you. They climb coconut trees to get to the coconuts, but being a little clumsy, fall out of the tree sometimes.
One of coworkers was pinched by a young, 1.5 cm long coconut crab still in a scavenged snail shell when we were at the beach in Kwajalean. But I know that's not what you meant.
That's why it's called the "coconut" crab.
I wonder if it's ever attacked human beings -- you know, like people napping at the beach.
Nature never ceases to amaze me.
PS. If you enjoy reading about "odd" creatures, check out "WTF, evolution?" at https://wtfevolution.tumblr.com/