I guess it's important to be a contrarian in this thread. I am a lawyer (although I acknowledge I have practiced very little in employment law), and to the best of my knowledge and belief, the practice described in the article is legal in the majority of states of the United States and perhaps in plenty of other places. I suppose it's more of a matter of opinion whether asking someone whom you didn't name specifically on your application as a reference is "ethical" or not, but it's simply a matter of fact that your whole reputation in the workplace may be of interest to the next person you work for or work with. AFTER EDIT, ADDITION TO THIS PARAGRAPH: A reply posted as I was replying helpfully refers to a website

http://www.crimcheck.com/resources/job-reference-shield-laws...

that summarizes some tips for employers about what they can say in response to requests for reference checks. The short summary of the various state laws is that employers can tell the truth. No employer may lie, but in general someone who knows you through an employment relationship is permitted to truthfully answer questions about your work, and you have no legal ground to sue the person who answers reference check questions (whose identity, as a practical matter, is likely to remain unknown to you).

I'll give an example of the hiring practice of one large (137 million dollars of revenue per year) organization in my town. The organization, which happens to be my friendly local public school district, has for more than a decade checked out candidates to be district superintendent by having resume-checkers telephone the references listed on the candidates' applications. The reference-checkers follow a protocol developed by a hiring practices consultant to conduct the reference check, and one question on the protocol is "Do you know anyone else who knows this candidate?" That person will be called, and the same question is asked, among all the other reference-checking questions.

The school district chief personnel officer, in a report to the school board just last month, mentioned that now a practice like this is followed for all new hires of teachers in the school district. The goal is to talk to multiple third-order references for each new person hired by the district. Going two degrees of reference out from the original references, and asking the right questions, does a lot to distinguish the best candidates for the job, in the personnel director's opinion. The practice mentioned in the submitted article, where the interviewer uses the candidate's self-disclosed social network information to find second-degree and third-degree references, seems fully legal and similarly likely to turn up more information about a candidate than just contacting the references mentioned by the candidate.

The school district chief personnel officer noted that when teachers are separated from our district's employment for poor performance, it is rare for anyone ever to contact our district even to verify the barest details of the teachers' job performance. So it appears that some organizations still don't check references or employment history at all. That is the organizations' choice, but it should hardly surprise a job candidate that some organizations check work histories very carefully, especially for positions of great responsibility like teaching young people. It is EXPENSIVE to make a hiring mistake for any organization, so quite a lot of time and effort is justified in making hiring decisions carefully.

In an earlier reply in another thread 58 days ago,

http://news.ycombinator.com/item?id=3148100

I linked to some external sources about legal reference-checking practices that I'll post here again as information for fellow Hacker News participants:

http://hiring.monster.com/hr/hr-best-practices/recruiting-hi...

http://www.drgnyc.com/list_serve/Jan24_2005.htm

http://www.acadweb.wwu.edu/hr/Employment/InfoForHiringOffici...

http://www.best-job-interview.com/reference-check-questions....

http://www.k-state.edu/hr/employment/referencecheck.htm

http://pbsbo.ucsc.edu/personnel_payroll/staff/recruit/ref_ch...

http://www.bridgestar.org/Library/HiringToolkit/ReferenceChe...

http://jobsearch.about.com/od/referencesrecommendations/a/re...