indianbill linked to a blog post by FB, saying they detect them by a footprint. However, in that same blog post, I read this first. "With billions of pieces of content being shared on Facebook every month and bad actors constantly targeting the people who use Facebook, preventing spam isn't easy. Just as a community relies on its citizens to report crime, we rely on you to let us know when you encounter spam, which can be anything from a friend request sent by someone you don't know to a message that includes a link to a malicious website." So, the debate is now open.