Are they really secret?
In a confidentiality agreement, don't refer to your customer lists or
customer database as secret, and then act like they're not secret. Your
practice counts for a lot if you want to sue the now ex-employee under the
Illinois Trade Secrets Act.
Hence the need to put systems in place to show your jealous guarding of secrets. Is access to this information encrypted, or otherwise secured? Who has access to customer information at the company? How do you reinforce the secret nature of the information, starting from the date of hire through orientation and beyond? How much do you actually invest in hiding customer information from view?