This is an example of a real ethical problem. You might be surprised to learn that there aren't all that many "real" ethical problems. Most of the ones that are proposed are pseudo-ethical problems.
In this case, an article from BBC News describe how Adoptees use DNA to find surname.
Male adoptees are using consumer DNA tests to predict the surnames carried by their biological fathers, the BBC has learned.Why is this an ethical problem? Because it (potentially) involves a conflict between the wishes of two individuals. The adoptee wants to know who his biological parents are and the biological parents may wish to remain unknown.
They are using the fact that men who share a surname sometimes have genetic likenesses too.
By searching DNA databases for other males with genetic markers matching their own, adoptees can check if these men also share a last name.
This can provide the likely surname of an adoptee's biological father.
As far as I'm concerned, the wishes of the biological parents have to be respected but with the widespread use of commercial DNA testing services, this wish can be circumvented by a determined adoptee.
Incidentally, these tests are also going to reveal who isn't your father, and that's also a problem.
There are many blogs acting as cheerleaders for the new commercial DNA testing services. One of them, The Genetic Genealogist seems to think that finding out who your father is, or isn't, is a good thing. That blog even points to a commercial company runnnig a program for adoptees with a success rate of more than 30% [More On Revealing Surnames Using Genetic Genealogy].
I think it's about time we started to think about the consequences.