Just four fairly vague pieces of information -- the dates and locations of four purchases -- are enough to identify 90 percent of the people in a data set recording three months of credit-card transactions by 1.1 million users. If someone had copies of just three of your recent receipts -- or one receipt, one Instagram photo of you having coffee with friends, and one tweet about the phone you just bought -- would have a 94 percent chance of extracting your credit card records from those of a million other people. This is true, the researchers say, even in cases where no one in the data set is identified by name, address, credit card number, or anything else that we typically think of as personal information.

Source: Privacy challenges: Just four vague pieces of info can identify you, and your credit card