I magine this. A notorious multinational is on the lookout for new business. For the sake of argument, let's imagine it's Lockheed Martin, the defence, security, and "advanced technology" corporation that has lately been seeing to the census . From somewhere in their R&D division comes an idea: "personal lifestyle security services" for millions across the planet. The wheeze is simple enough: sign up and hand them your personal correspondence, financial records, bank details, ID documents, and more. They'll have all your stuff, and you'll have a unique password whenever you want a look. And just think: more clutter shunted out of your life, leaving you to glide through the minimalist bliss of 21st century living.

You would have to be out of your mind. But this is the world we are hurtling towards, although it's not defence conglomerates who are in charge ? yet ? but private technology giants. The key is cloud computing , whereby just about anything that can be digitised is stored in remote servers, leaving us to access it from wherever we fancy. If you have a Gmail or Hotmail account, you'll already be a practised cloud user. Two years ago, David Cameron suggested that Google and Microsoft might be involved in the cloud-based storage of people's NHS records ; now the Department of Health appears to have plans for exactly that. In 2009 the worth of cloud computing was put at $58.6bn; by 2013 it's forecast to reach $150.1bn.

The new world is, of course, less a matter of clouds than data centres: huge impersonal sheds in which servers whirr away, while millions log in and out ? a turnabout with an intriguing circularity. Up until the late 20th century the history of the industry was partly the mass transfer of data from hulking mainframes to ever smaller personal computers. Now the momentum is in the other direction, and what you might think of as digital centralism is back, in a world awash with prying governments, hackers, corporations that seem as prone to skulduggery as they ever were ? and terrorists who may well eye data centres as mouthwatering targets.

So why aren't we worried? Inspired branding undoubtedly does its work. First, there is the term "cloud computing" itself, whose uncertain etymology is less important than its implicit suggestion of an innovation with all the unremarkable ordinariness of the weather. Consider also the cuddly, kids'-TV-esque Google logo , or the way that so much of the Microsoft brand is synonymous with the humanitarian work of Bill Gates . All this chimes with a culture in which, as supposedly maverick organisations get ever closer to government, mass trust in their operations still seems to know no bounds ? even when such revelations as the iPhone's surreptitious tracking of its users' movements point to slightly more on their minds than the breezy convenience of their customers.

While we're here, take note: all messages on Gmail are automatically scanned so Google knows where to place any relevant ads ? and deleted messages and accounts " may take up to 60 days to be deleted from our active servers and may remain in our offline backup systems ".

Inevitably, hacking into stuff stored in the cloud is a global pastime, with its own grim star system. Earlier this month, for instance, a very unpleasant Californian named George Bronk was jailed for six years for rifling through Gmail and Yahoo mail accounts belonging to women and girls (some of them British), and sending any revealing pictures he found to all their Facebook contacts. Meanwhile the world's more authoritarian states know exactly what the cloud allows them to do: in late 2009, for instance, Google's servers were breached by Chinese hackers, presumed to be under government orders, who tried to break into the email accounts of human rights activists .

We all know how even democratic states tend to view the kind of informational riches that the cloud contains. Our own Regulation of Investigatory Powers Act is in the process of being partly reformed, but even more invasive data-gathering powers seem in the pipeline. In the US, whether to drop or renew provisions in the infamous Patriot Act is currently the subject of a noisy debate ? but extensive powers to pry into data and communications will remain. ( In Canada this has fed into a fascinating debate about public and private sectors using US-based cloud services, and thereby leaving people open to American surveillance.)

There is, perhaps, a worrying time lag at work here. The computer industry came of age in the 1990s, that giddy phase of American and European history when authoritarianism was assumed to be on the wane. For sure, it's still nice to live in a liberal democracy, but given that the world has since moved in no end of sinister directions, isn't our unthinking embrace of the cloud (and just to recap: our medical records could soon be up there) an ill-advised throwback? And what of the long view: looking ahead 50 years, how certain are we that the surveillance state will not have extended its tentacles; that nasty, illiberal politics will not be all the rage; or that Google , Microsoft et al will not have learned dangerous new tricks?

Right now, I think of the hyper-connected activists behind UK Uncut, or the ongoing anti-fees protests, or the other campaigns over which our spooks presumably keep watch, and feel a pang of unease. This cloud, I fear, may yet turn very dark indeed.