Square, the mobile payment company started by Twitter co-founder Jack Dorsey, just broke 2 million users, just six months after it surpassed 1 million.
The company is now processing more than $6 billion in payments as well on an annualized basis. That figure represents huge growth for Square. Last year at this time, the company was hoping to process $1 billion in payments "within the next year."
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The latest milestone comes after a busy few months for Square. The company expanded its payment option to New York City taxis and introduced a cash register iPad app this spring as it fended off a challenge from PayPal, which launched its own mobile payment solution.
The company's vision has also been rewarded by investors, which have plowed $138 million into Square, giving it a valuation in the $4 billion range.
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This story originally published on Mashable here.