[BigO]

Only thing I can think of would require uploading malicious software with a modified version of the square device but that doesn't look possible, yet. Why not just use your phone to pay, for example the business owner gives you a qr code that you scan in then use an app that interfaces with your paypal account that pays the business they get confirmation you don't have to worry about using extra hardware, or why can't the business owner give you a number to text and then collect payment through that then you don't even need a smartphone any cellphone will do. Really things would be more secure if I could send money to an account rather than have them remove money from mine.