[alexcason]

"The ads would come through a Facebook program called "Custom Audiences," which lets a business upload lists of customers and phone numbers or other contact information the business has collected from warranty cards or other sources. Facebook matches the list to users with the same information and shows them ads. Facebook says it doesn't give out users' information to advertisers."

What happens if the advertiser uploads only one phone number to their campaign? Will they then know for certain if the one user clicked on the advert?