Update: someone pointed out that PayPal actually reveals the last four digits of the phone numbers, so this technique may work for large countries as well if the target has its phone linked to its PayPal account.

Last month, I discovered it is relatively simple to reveal private phone numbers on Facebook, uncovering some phone numbers of Belgian celebs and politicians. Even though this trick only seems to work in small countries such as Belgium (+/- 11.2 million people), a significant number of people is affected by this simple, yet effective privacy leak.