Two computer discs containing names and addresses of more than 7,500 motorists in Northern Ireland have been lost.
The information was not encrypted and went missing at a sorting centre in Coventry in England.
The material had been sent from the Northern Ireland Driver and Vehicle Agency in Coleraine, Co Derry, to the Driver and Vehicle Licensing Agency in Swansea.
The Department of the Environment in Northern Ireland, which runs the Driver and Vehicle Agency, confirmed the discs had been lost.
A special telephone helpline had been established for those affected.
Letters have been sent to all registered keepers of vehicles involved.