I’m not sure I would classify this as the "cleverest" scam, but I’m sure it has been successful. Similar scams (socially engineered phishing) have been around for a long time. Site’s where to have an account, they don’t need you to verify private details; most certainly not when they are about to "delete your account.
Cleverest Facebook scam yet threatens to DELETE account…. unless you hand over details | Mail Online
OSG: Bits, Bytes and Packets 