The red-hot microblogging tool previously raised rounds of $15 million and $5.4 million. In a blog post, Biz Stone of Twitter writes, “We weren’t actively seeking more funding because significant capital from last year’s partnership with Bijan and his team at Spark is still in the bank. Nevertheless, our strong growth attracted interest and we decided to accept a unique opportunity to make Twitter even stronger with a very attractive offer.”

And while that money buys Twitter more time to actually generate revenue, Stone assures us that is also in the works. “We are now positioned extremely well to support the accelerating growth of our service, further enable the robust ecosystem sprouting up around Twitter, and yes, to begin building revenue-generating products,” he writes.

In any event, while the business model remains a mystery, it’s clear Twitter is in it for the long-haul, and despite onlookers constantly questioning how they’ll make money, the company still has plenty of time to figure it out, on their own schedule.

Update: VentureBeat reports that the amount raised was $35 million.

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