Is Phone-based Two Factor Authentication Secure?

Gmail two factor authentication requires you to enter an SMS sent to your handphone before you can use Gmail on a new computer. This means that hackers needs to have your hand-phone and password before they can access your Gmail.

Sounds secure? Guess what, Grant Blakeman’s Gmail account was hacked in 2012 even though he had two factor authentication turned on.
Read How Hackers Reportedly Side-Stepped Google’s Two-Factor Authentication in Gizmodo.

Hackers must have discovered his password, and his phone calls were forwarded to a different number by hackers who had persuaded Grant’s cellphone provider…