Nearly two-thirds of marketing professionals have lost consumer information over the past two years, and in 90 per cent of cases the loss or theft went unreported.
The figures are from the 2008 UK Study on Email Marketing Practices & Privacy conducted by the Ponemon Institute for email marketing firm StrongMail.
One of the key reasons for the data breaches is the marketing sector's tendency to outsource various functions to third-party companies.
However, many of the incidents went unreported as those involved believed that they were under no obligation to report the incident to the affected customers.
"A cavalier attitude towards outsourcing customer data to third parties, combined with complacent processes for keeping the data safe, is a recipe for disaster," said Paul Bates, managing director of StrongMail UK.
"Confidential customer data does not travel well and providing it to third parties for outbound marketing purposes can be a risky proposition.
"This data is extremely valuable to most firms, and we advise them to think very carefully about how they keep it safe."
The survey also found that email marketing poses a big risk to the privacy of UK consumer data, ahead of internet, telemarketing and direct mail outbound marketing channels.
Among those UK firms that outsource their email marketing, the incidence of data breaches rises from 61 per cent to 78 per cent.
The flippant treatment of personal data for marketing purposes has prompted security firms to call for greater government action to protect data.
"These results highlight how exposed consumers are in regards to the confidentiality of their personal identifiable information," said Paul Davie, founder of database security firm Secerno.
"Everyone should have a transparent view of who holds their data, and what information they have, similar to that of a credit check which at present is overlooked.
"It is inexcusable that the government continues to drag its feet on breach disclosure legislation, especially since best practice is not being followed by so many organisations handling sensitive and personal consumer data."
However, Larry Ponemon, founder of the Ponemon Institute, and author of the study, stressed that the findings are not all doom and gloom.
"Although 60 per cent of UK marketers outsource their email marketing, 65 per cent would consider in-sourcing their campaigns to ensure greater protection of personal data," he said. "The message is slowly getting home."
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