INDIANAPOLIS -- Someone who hacked the state government's Web site may have accessed credit card numbers of 5,600 residents and businesses, the Indiana Office of Technology said Friday.

In letters sent to the 5,600, the state said that the credit card numbers were unencrypted because of a technical error and that the hacker may have viewed them.

The letter says that the problems have been fixed. The state is asking those who receive the letter to review their credit card statements and report any questionable activity to credit companies.

"Know that we are working our tails off to not allow these kinds of security events to occur in the future," the Office of Technology's Chris Cotterill said.

The people whose numbers were exposed include those who made transactions at the state's Web site in January, such as Bureau of Motor Vehicle customers and hunters who were renewing licenses.

Officials said they don't know whether the hacker has used the exposed numbers.

The state said the Secret Service and credit card companies have been told about the breach and that the compromised credit card numbers have been placed on a list to be watched for potential fraudulent activity.

Anyone who receives the letter is asked to call the Indiana Web Site Security Hotline at 888-438-8397 for additional information.