McAfee’s auditor Deloitte & Touche USA LLP has lost an unencrypted CD containing the personal details of more than 9,000 of its employees.
The auditor lost the CD when one of its employees left the disc in the back of an airline seat.
Security software company McAfee was informed of the incident by Deloitte on 11 January, almost a month after the disc was lost.
The disc was lost last December and McAfee has just finished sending out warning letters to the employees and former employees affected.
The back-up CD contained the names, social security numbers and information on stock holdings held by 9,300 of McAfee's current and former US and Canadian employees.
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All those affected by the data loss are being given two years' worth of free credit reports by credit bureau Experian, to make sure they do not become the victims of identity theft.
McAfee sells its own product to allow users to easily encrypt files. Deloitte may well now be tempted to use it.
The data loss is the latest to hit corporate America, including big losses at Bank of America twice, and credit rating company ChoicePoint.