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Ballmer was speaking in Australia at Telstra's annual investment day, where he questioned the financial model underpinning the technology.

"I don't really understand its [Google's] strategy. Maybe somebody else does. If I went to my shareholder meeting, my analyst meeting and said, hey, we've just launched a new product that has no revenue model! Yeah. Cheer for me. I'm not sure that my investors would take that very well. But that's kind of what Google's telling its investors about Android," said Ballmer.

He also questioned the assumption that by giving away the operating system Google was getting to put its search on devices for free. According to the Microsoft chief executive, operators will still ask to be paid to carry search.

He also questioned where the long-term commitment to improve the operating system would come from without a financial plan underpinning it.

"Google doesn't exactly bubble to the top of the list of the top competitors we've got going in mobile," Ballmer concluded. "They might some day. But right now..."