Current cloud services and traditional Web sites like Amazon or Azure or Google or Facebook all are centralized from the management point of view and thus, they suppose a threat as big as a Super-Mainframe would pose for privacy and security of the data as well as the computing power. Amazon could paralyze the entire world. Facebook can be perfect for political campaigns if the right "leaks" happens when they need them. we know it very well.
The source of concern are:
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The centralized databases that consolidate all the data of all users instead of letting the user to control where to store his own data wether locally or in other's nodes and define his own access policies. Although centralized databases are also a consequence of other concerns depicted below, centralization of data is something desired, since it is very profitable for legal and -I´m worried- criminal uses of such data.
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The methods for obtaining scalability apparently demand farms of computers, again