Most of the services we tested use genotyping to read your DNA. Genotyping looks for specific markers in your genetic code. For something like ancestry testing, genotyping is effective because it identifies known variants in your DNA. Scientifically speaking, genotyping’s weakness is that it can only recognize previously identified markers. This is one reason DNA tests’ accuracy relies so heavily on the DNA database size; there must be enough information available and identified genetic variants in the database to recognize new customers’ markers.

For our evaluations, we assembled a group of testers willing to spit into a tube on camera. We chose four individuals of varying backgrounds. Two had previously taken one or more DNA ancestry tests, and two had not. Two had fairly well-documented family histories to compare against, one was adopted, and one had information about one side of the family, but not the other. All of us took DNA tests from AncestryDNA, 23andMe, National Geographic and Family Tree DNA. One tester also took each of the five additional tests we reviewed. After collecting spit and cheek cells, we mailed all of the tests at the same time and waited for results, noting all communications from the company in the meantime and how long it took each service to notify us that results were ready to view. We collected data based on testers’ impressions of their results, each service’s features and extras, how easy it was to use and navigate the service’s website, along with several other factors. We added this testing data to rigorous research and information gleaned from conversations with representatives from Ancestry, 23andMe, MyHeritageDNA, LivingDNA, Humancode (now owned by Helix) and 24genetics. 
Once your genetic information is out there, it’s difficult to undo. Also, once you know something about yourself, it’s impossible to un-know. Revelations such as having different parents than you expected or finding unknown half-siblings are difficult to process at any age, but it’s particularly troubling for kids. However, you can always simply opt out of family matching features.
WARNING: AncestryDNA highly discourages the purchase of our DNA kit from unauthorized resellers. To ensure the best experience and service, please purchase directly from AncestryDNA. DNA kits that are fraudulently purchased and then resold through Amazon may be deactivated by AncestryDNA, and may not be eligible for a refund. Before you can use AncestryDNA and see your results, you must create an Ancestry account and agree to Ancestry's Terms and Conditions and Privacy Statement. Actual product packaging and materials may contain more and different information than what is shown on our website. We recommend that you do not rely solely on the information presented and that you always read labels, warnings, and directions before using or consuming a product.

If the company responsible for running your test is sold, whatever you signed loses significance due to the privacy policies of the company. Despite most of these privacy policies stating they will notify you of any changes, you would have to keep in constant contact with the company to ensure you were actually aware of these changes. The people willing to do this would be far and few between. Unfortunately, even if your name is not located within the database, this does not mean other databases cannot be used to determine your identity. In one specific case, a woman had a DNA test run. She found out she had a half-sibling. Although she was very excited about this news, this type of information would devastate numerous individuals.

Molly K. McLaughlin is a New York-based writer and editor with more than a decade of experience covering technology. She has tested and reviewed all sorts of software, mobile apps, and gadgets. Before launching her freelance business, she was an editor at PC Magazine, covering consumer electronics, followed by a stint at, a revie... See Full Bio
The companies providing ancestry DNA tests are making most of their money from selling the genetic information as opposed to running the tests. Companies purchase this information to increase the size of their genetic databases. Nearly half the companies selling ancestry information are selling to more than just one company. These are sometimes pharmaceutical companies attempting to understand how specific human genome sections can help develop new drugs. Certain mutations will impact the effectiveness of these drugs. The original DNA sample is only destroyed by roughly ten percent of these companies. Most companies keep or sell the sample. This means it is both your data and saliva being sold.
It’s easy to do these tests; it’s usually just a case of collecting your own samples at home, filling in short, basic questionnaires, posting the packages, and then logging on to interactive websites for confidential results (all the kits I tested used outside laboratories). With an array of price ranges and options, from one-off DNA-blitzes to targeting specific health areas, to fitness/wellness tracking, it’s no surprise that these kits are proving to be very big business and the field is primed to get even bigger, with a global market estimated to be worth around £7.7bn by 2022.