Security researchers discovered vulnerabilities in mobile card readers. That's the word from a pair of security researchers, who discovered that mobile payment systems had vulnerabilities that could let hackers steal credit card info or change the value of what people pay.Researchers Leigh-Anne Galloway and Tim Yunusov of cybersecurity company Positive Technologies revealed their findings at the Black Hat security conference in Las Vegas on Thursday. Researchers estimate that 46 percent of all noncash payments will be done through a mobile reader by 2019.Galloway and Yunusov looked at readers from the most popular mobile point-of-sale, or mPOS, providers in the US and Europe: Square, PayPal, SumUp and iZettle. The vulnerability opened up various possibilities for merchants to steal from customers."It's possible, if you were a fraudulent merchant, you could change the transaction value to make it a higher value than what's displayed on the reader," Galloway said in an interview before Black Hat.