But somehow the back office software business manages to mint more than its share of the super-rich, it seems.

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QuickBooks has more than 90% retail market share for small business accounting software.

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That is why, as the stock market hemorrhaged when trading resumed after the tragedy, the share price of Viisage, a maker of facial-recognition software, more than doubled, the biggest gainer of any stock that grim day.

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Any share you give up today may be worth more tomorrow, says Didier Moretti, chief executive of Annuncio Software, a Mountain View, Calif. firm that automates Web marketing.

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Microsoft's commitment to PC technology has kept it investing in operating system and office automation software for the last decade while losing more than two-thirds of its market share in smartphone operating systems and delaying its entry into the fast-growing tablet business--places where Apple has had astoundingly profitable revenue growth.

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ArcSight had actively sought acquirers, and HP, rather than continue to resell software from ArcSight competitor SenSage, may have simply seen an opportunity to buy more market share and a source of new growth.

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