How do I stop an ex-employee from using our confidential information?

Employees owe a duty of confidentiality while employed, and this continues after employment in respect of genuine trade secrets and confidential information, even without a written agreement. A written confidentiality clause and a reasonable restraint of trade clause add further protection. Start by gathering evidence, such as logs of file access and emails, and preserve your systems. You can send a letter to the former employee reminding her of her obligations and asking for the return or deletion of information. If there is a real risk of ongoing misuse, apply to the court for an urgent interim injunction and orders for delivery up, and possibly damages. Courts distinguish between confidential information and an employee's general skill and knowledge, so obtain legal advice about the strength of your case.