You may think twice about participating in a genetic study. Science magazine makes the point: If you have been ever been profiled by a SNP scan that is now (even anonymous) in the public domain, every further study (or anyone else who has access to trace amounts of your DNA) can re-identify you by 20 – 70 characteristic SNPs. This is even problematic as likelihoods for your disease risk can be calculated from SNP arrays of distant relatives, yea, yea.