A 'survival clause' that would guarantee destruction of your data in case the company goes out of business would be a minimum here.
But instead, 23andme says in their privacy policy:
"We may use Genetic and Phenotypic Information to conduct 23andMe-authorized scientific research and development. Any Phenotypic Information you provide is done on a voluntary basis. We may provide third party organizations access to this information for scientific research, but without your name or any other Account Information."
And that's the kicker, so your full genome gets sold to some 3rd party (you don't even get to know who) and all they do is strip off the 'meta data' regarding your person.
And AOL and NETFLIX have already shown that anonymization of data is a myth.
Your DNA is your identity. It just hasn't been tied to the meta data of your name, address and social security number, but again, with a bunch of confirmed identities of relatives that is a job that is probably doable.
I'm not good enough at math to give you the percentage of a certain population in order to be able to infer the rest, maybe someone else here can do that.
But given a population size 'n' if you get a random distribution of individuals and you know their genes and you know have a graph of relationships (say through facebook or some other means of tracing links between people) you should be able to make a formula that tells you what kind of 'coverage' you can expect based on how large a sample.
First of all, today, this is not full genome information, just your genotype. Second, if we want good molecular medicine, information like this is essential (some might argue the only way) to get good sampling and do the appropriate research.
Addendum since I can't reply to the comment. They don't quite have the technology on hand today to do full genome analysis today. I am not sure there is enough material to do whole genome sequencing with current technology (I could be wrong).
That's what they give you. But you give them your full genome.
You seem to be pretty knowledgeable here, how much information is still present in those SNP maps (in terms of bits per person)? Would an SNP map still uniquely identify an individual ?
This is also the basis for DNA forensics/paternity tests. If you sample enough SNP locations you should theoretically have a unique signature (this is where you get the courtroom statistic of 1 in 3 million)
[Disclosure: I participated in public health genomics research in grad school.]
Business Transitions
In the event that 23andMe goes through a business transition such as a merger, acquisition by another company, or sale of all or a portion of its assets, your personal information and non-personal information will likely be among the assets transferred. You will be notified in advance via email and prominent notice on our website of any such change in ownership or control of your personal information. We will require an acquiring company or merger agreement to uphold the material terms of this privacy statement, including honoring requests for account deletion.
And what about all those companies that have received copies of your genetic data from 23andme in the meantime, and their survival clauses?
I don't think it is possible to do this in a watertight way.