“Don’t be evil” was the mantra of the co-founders of Google, Sergey Brin and Larry Page, the graduate students who, in the late 1990s, had invented a groundbreaking way of searching the web. At the time, one of the things the duo believed to be evil was advertising. There’s no reason to doubt their initial sincerity on this matter, but when the slogan was included in the prospectus for their company’s flotation in 2004 one began to wonder what they were smoking. Were they really naive enough to believe that one could run a public company on a policy of ethical purity?

The problem was that purity requires a business model to support it and in 2000 the venture capitalists who had invested in Google pointed out to the boys that they didn’t have one. So they invented a model that involved harvesting users’ data to enable targeted advertising. And in the four years between that capitulation to reality and the flotation, Google’s revenues increased by nearly 3,590%. That kind of money talks.

Rana Foroohar has adopted the Google mantra as the title for her masterful critique of the tech giants that now dominate our world. It’s an apt choice because it captures one of the leitmotifs in the story of how these corporations came into being and grew to their current monstrous proportions, a journey that takes them from naive (and sometimes libertarian) beginnings to ruthless monopolistic dominance.

The great thing about her book is that it breaks the mesmerising spell that the tech giants seem to have cast upon governments, mass media and users everywhere. The beginning of wisdom in this matter is to realise that Google, Facebook, Apple, Amazon, Netflix, Microsoft, Uber et al are just very large corporations that do what corporations have done from time immemorial – exploit resources in order to generate profit. The only differences between them and the corporate giants of old are the nature of the resources they have appropriated and the grotesque profit margins that they obtain.

Foroohar is well qualified to tackle them. Her day job is that of the Financial Times’s global business correspondent, so she occupies an influential perch. But she has also, in her time, worked on the fringes of the tech industry during the first internet bubble, the one that burst in 2000. So she’s seen the dynamics of tech exuberance from the inside.

It is about the essential sociopathy of corporations, even those run by well-intentioned human beings

Basically, though, she comes across as a level-headed, informed and well-connected journalist: most people in the industry return her calls, even if they make sure to have a PR adviser listening in. Which is prudent, since Foroohar combines a polite manner with a high-powered crap-detector. She even emerged sane after spending several days in the company of Travis Kalanick, the founder of Uber and a character whom James Joyce would have described as “a caution to rattlesnakes”.

The overarching theme of Don’t Be Evil is “how big tech betrayed its founding principles”. This is a variation on a popular theme: how the people who founded these powerful corporations were basically high-IQ innocents who had their innocence and idealism knocked out of them by the exigencies of running capitalist organisations.

The “don’t be evil” mantra is one example. Another is Mark Zuckerberg’s tropes about “connecting the world” and creating “communities”. Another is Steve Jobsʼs metaphor of the personal computer as “a bicycle for the mind”. And of course there’s the pervasive mysticism about using technology “to change the world”. At no point in these vapourings does one ever find crude intentions of becoming insanely rich.

There is another way of reading this story, though. It is about the essential sociopathy of corporations, even those run by well-intentioned human beings. The reason some of the tech companies got such an easy ride in the public imagination is that their founders were not middle-aged bastards in homburg hats – think John D Rockefeller and JP Morgan – but young geeks in hoodies. Yet these same geeks supervised the growth of corporations that are as ruthless and socially irresponsible as Standard Oil was.

Which means that we now find ourselves faced with the same problem as faced the United States in the early 1900s: how to bring these behemoths under democratic control. And one of the most useful things about this book is that it does not fall into the trap of regarding all the tech giants as being the same. They’re not and discriminating between them will be the key to regulating them. The business model of Facebook and Google, for example, is radically different from those of Apple or Microsoft. And Amazon is a case apart.

The most startling thought that emerges from Don’t Be Evil, though, is that big tech may have already become “too big to fail” because the companies have become systemically critical to our economies – for reasons that have little to do with technology. The risk comes from the colossal “cash” reserves that they have parked abroad in best tax-avoidance manner. Foroohar says that more than half of those stashes are denominated not in dollars, but in corporate bonds. And if anything should happen to the value of those, then it might be 2008 all over again, but without a safety net. So much for not being evil.

• Don't Be Evil by Rana Foroohar is published by Allen Lane (£20). To order a copy go to guardianbookshop.com or call 020-3176 3837. Free UK p&p over £15, online orders only. Phone orders min p&p of £1.99