there are many ways to skin this cat if one was motivated enough to put their mind to it... but some suggestions anyway: never have 700M profiles in one place.

there are many ways to skin this cat if one was motivated enough to put their mind to it... but some suggestions anyway: never have 700M profiles in one place. decentralization by default - large scale centralization only when absolutely needed and with rigorous controls as a public (or highly regulated) good. never create portable / tradeable behavioral profiles that can be linked to individuals. what can happen will happen and is happening. never offer trivial free services in exchange for significant private data. establish a respectful and healthy client/user relation without hidden third parties in the loop