The 305 staff at the Department of Works and Pensions Call Centre at Pembroke Dock have had their identities stolen by organised gangs.
Hackers have accessed part of the department's computer payroll system which stores national insurance numbers, dates of birth and bank details of more than 1,500 staff at Pembroke Dock, Harrow, Belfast and Glasgow centres.
At Pembroke Dock alone, 98 of the 305 staff have already had confirmation that their details have been used for child tax credit frauds and there are fears that others may have their identities used to obtain credit cards and loans.
The online tax credit application system was suspended last week so that new security checks could be developed It is believed that hundreds of multiple online applications were made from internet cafes using false identities.
One Pembroke Dock staff member who does not wish to be named said:
"We have all had letters advising us to check with the child tax credit department and we have also been told to contact CIFAS - the Identity Fraud Protection registration company - and Experion the credit checking agency.
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