The preferences of 444,031 organ donors were recorded wrongly on the Organ Donation Register (ODR) because of a software problem.
The Information Commissioner's Office (ICO) said in March last year NHS Blood and Transplant (NHSBT) found irregularities between the organ donation information on Driver and Vehicle Licensing Agency (DVLA) application forms and the information recorded on the ODR.
It was then discovered that an ODR software error in 1999 had caused problems recording organ preferences from the DVLA.
"Whilst the vast majority of the data remained accurate, it was discovered that the details of over 400,000 people required correcting, while a number of other patients had to be contacted directly in order to ensure that their original preferences remained intact," said the ICO.
Mick Gorrill, Head of Enforcement at the ICO, welcomed the NHSBT's commitment to correcting the inaccurate data and "their willingness to make sure this type of incident does not happen again by introducing a variety of new security measures".