According to the BBC report, the database sat unsecured for as long as 10 months as a result of human error, and the breach was not the result of a cyberattack.
The telecoms firm admitted the exposed information had been accessed at least once by an unknown third party.
Virgin Media CEO Lutz Schüler elaborated on the incident, claiming the company shut down database access as soon as it learned of the mishap.
“[The database] contained some contact details of approximately 900,000 people, including fixed line customers representing approximately 15 per cent of that customer base,” he said.
He added that no passwords or payment data was compromised, but names, home and email addresses and phone numbers were listed in the database.
The company has said it has notified the affected customers via email, warning them of potential phishing or fraud attempts.