Strict controls are needed to ensure genetic information collected for research is not used inappropriately by outside parties, experts have warned.
Many DNA databases have been collated for specific studies on genes and disease, a British Society of Human Genetics meeting in York heard.
But pressure from other researchers to access the data puts patient anonymity at risk, experts warned.
Safeguards to protect patient data are imperative, speakers said.
Professor Marcus Pembrey, an expert in paediatric genetics, said there was increasing pressure from organisations funding the research to let other people see the information.
But the original research team needed to retain control in order to maintain the trust of those who agreed to take part in the study, he said.
There is a real risk that data, which is supposed to be anonymous, could be made available on the internet if researchers are allowed unrestricted access, he warned.
Professor Pembrey, who was involved in two large UK genetic studies - the Children of the 90s study and the 1958 British Birth Cohort - said the information can be made available for other research teams through collaboration and careful anonymisation.
"The success of such research is based on the trust between the study participants and the team responsible."
He added that participants also entered in the knowledge they would not be told about their genetic results.
"That makes us even more convinced it's essential there isn't inadvertent disclosure of the results on the web.
"The worry is there is a trend coming from pressure from the funders saying that all scientists should have unfettered access."
Professor Pembery has been involved in advising projects such as the UK Biobank, a Department of Health and Medical Research Charity-funded project of 500,000 people aged 40-69, which has just begun recruiting.
He added that "genuine benefits" of such research should not be undermined by lack of public trust in what was happening to their samples.
Professor Rory Collins, chief executive officer and principal investigator of UK Biobank, said in the consent form they were explicit about how the samples would be used.
"It is entirely clear that this information will be available to bone fide researchers whether they're academic or commercial."
And no identifiable information about participants will be available to anyone outside of UK Biobank.
Professor Steve Bain, a member of the Human Genetics Commission, said much greater consideration had gone into databases put together for research purposes than for the national DNA database used for forensic purposes.
Also speaking at the British Society of Human Genetics meeting in York, he said ethics of the national DNA database was only just being discussed despite it being in place for many years.
"When you have research you have to go through the ethics committee and that's always been the case."