Scientists have described some services provided by companies tracing ancestry using DNA as akin to astrology.
Some test findings tell people that they have links to groups such as Vikings, to particular migrations of people and sometimes to famous figures such as Napoleon or Cleopatra
But researchers working with a campaign group say DNA tests cannot provide accurate information about ancestry.
Ancestry companies insist they are able to provide a valuable service.
An increasing number of companies are offering to profile the genetic history of individuals based on a DNA sample for around £200.
But in a public guide, published by Sense About Science, Prof David Balding and Prof Mark Thomas of University College London warn that such histories are either so general as to be "personally meaningless or they are just speculation from thin evidence".
The scientists say that genetic profiles cannot provide accurate information about an individual's ancestry.
They say "the genetic ancestry business uses a phenomenon well-known in other areas such as horoscopes, where general information is interpreted as being more personal than it really is".
They also highlight uncritical media coverage of the issue. Prof Balding, says that news items about famous people being related to historical figures often come from PR material provided by genetic testing companies.
Prof Thomas says that the idea that we can read our ancestry directly from our genes is "absurd".
"This is business, and the business is genetic astrology," he said.
BBC News contacted five companies offering DNA ancestry services. We received a response from the DNA Worldwide group.
Their director David Nicholson told BBC News that all firms should not be tarred with the same brush. Some such as his, he argues, provide credible and legitimate services.
"With advanced testing you can provide a general ancestry indication i.e. Northern European, Western Africa or Middle Eastern and in some cases even more specific," said Mr Nicholson.
"DNA cannot tell you that your ancestors were Viking, simply that your ancestry came from a part of the world common to the Vikings based on historic facts. It's important to talk to the company who provide the testing to make sure your expectations are realistic".
Prof Steve Jones, from University College London and author of some of the seminal books on genetics and evolution, said: "On a long trudge through history - two parents, four great-grandparents, and so on - very soon everyone runs out of ancestors and has to share them.
"As a result, almost every Briton is a descendant of Viking hordes, Roman legions, African migrants, Indian Brahmins, or anyone else they fancy."