Whenever credit cards are involved, people are worried about security. Sending the credit-card data to a terminal via a radio signal might not seem very secure. But when the process operates properly, it's actually more secure than using a magnetic-strip credit card. The information on a magnetic strip can be read, altered or duplicated using a variety of devices that have been available for years. The encryption built into a blink card make this particular form of theft impossible. Also, using the blink card allows the user to keep the card in his or her hand the entire time. This could prevent someone from seeing the account number and name on the card.
A signature is not required when using a blink card, which leads to security concerns. Chase feels that the encryption and other security features built into blink make the card secure without the need for a signature, which would slow down the transaction and defeat the purpose of blink altogether. They even suggest that it makes the transaction safer, since the clerk never sees the card or account number. The problem, of course, is that if someone gets his or her hands on your blink card, there's no need to verify anything at all in order to use it in a store. But Blink users are no more accountable for fraudulent charges than any other credit-card user.
There have been reports of problems in the testing of contactless RFID credit cards, however, that lead to additional security concerns. In some cases, if two or more terminals were close together, not only did both terminals read the card, but the read range of each terminal increased to as much as 30 feet (9 m) [ref]. Even if the terminal is operating within the proper range of 4 inches, some people are worried that they could accidentally walk too close to a terminal and end up paying for someone else's purchase. The simplest safeguard against this is probably merchants positioning the terminals in such a way as to make this unlikely.
The worst case scenario involves someone getting their hands on a blink terminal and modifying it to increase the range. Potentially, someone could set up the terminal at a crowded location and collect the credit-card data of anyone who came within the terminal's read range. This probably won't be a concern at first, since few terminals will be available, but if the technology matures, blink terminals could fall into the hands of criminals.
There is a way to protect blink cards from giving out their information to unauthorized terminals, either accidentally or due to criminal activity. If the card is placed in a sleeve lined with metal, it will not function. If contactless credit cards become popular, expect to see "RFID blocking" wallets and purses on the market.