How can I find out if an employee copied company data?

You might want to get creative: set up a fake customer with an email diversion going to one of your private accounts. Use a family member's number as the business number to see if anything gets mentioned. That way, if data goes missing, you’ll have a way to find out pretty quickly.

Talking to your security officer about this is a smart move. Almost every company I've been at, employees could have taken sensitive data if they wanted. What's your end goal here? Are you worried about someone stealing trade secrets? If you're asking for advice online, it might already be too late.

Consider setting up hard disk encryption on the company systems. Additionally, ensure that any data copied to external drives is also encrypted so it can only be accessed by the company's devices. This could help safeguard against data theft in the future.

This is a tough situation because it's hard to find solid proof after the fact unless you had monitoring in place before. You should start by checking any existing logs like Microsoft 365 audit logs, Defender, or any endpoint detection and response tools for strange file access, big downloads, USB usage, or cloud uploads. On the employee's device, you can look at recent files, PowerShell history, browser history, and even WSL activity—though that's tricky since it can be easily cleaned up. If you didn’t have data loss prevention (DLP) tools in place beforehand, it’s all about finding indicators rather than definitive proof. For future prevention, consider implementing DLP policies and monitoring tools to actually catch any suspicious activity before it happens. Just be mindful of privacy laws around checking personal data on their devices.