Ading in my voice for the open, TOTP (time-based, one time password) standard such as Google Authenticator, Authy, LastPass Authenticator, etc. SMS can be intercepted/hacked, and requires sensitive info be sent unencrpyted every time. TOTP sends the key once, then combines it with the time every 30 seconds for a new, endless supply of codes. Get serious about keeping our money safe, Paypal!
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