Sales of Microsoft’s flagship Windows software disappointed for the third straight quarter, taking the gloss off better than expected earnings that were aided by an unusually low tax rate.

The results failed to excite a market already wary about growth prospects for the company and PC industry as netbook sales give way to tablets. The stock was flat in after-hours trading.

The world’s largest software company posted net profit of $5.87 billion, or 69 cents per share, up from $4.52 billion, or 51 cents per share, in the year-ago quarter.

Microsoft was helped by an unusually low tax rate of 7 per cent in the quarter, that cut its tax bill by more than $1 billion from the year before, to $445 million.