If you suspect that your business has been a target of corporate espionage, it’s essential to take action immediately — from doing an in-house investigation to hiring a private professional. If you see any of the below signs, don’t ignore them, but also take care not to make any unfounded accusations or statements. Keep your thoughts closely held and get the evidence first.

1. Unexplained or sudden changes in practices

When staff members suddenly change how they execute established business practices, this could signify that they are also working for someone else. (Keep in mind that there could be other reasons as well.) And if you see an employee suddenly working more hours or coming in on the weekends, this could be additional cause for concern, as corporate spies may try to cover their tracks by doing this illicit work when they know they are less likely to be watched. So, when there are unexplained changes in behavior, and particularly when people act strangely when asked questions about them, take notice.

2. Changes in business relationships

If you stop working with a business partner and there is no apparent reason why, this could be because that person is involved in corporate espionage against your company. (Keep in mind that such a change is typically sudden.)

Related: 3 Reasons You Should Spy on Your Competition

3. Unusual computer activity

When strange activity on a company’s computers occurs, such as staff emailing more than usual or using their own devices more often to send messages or images, ascertain why. While such a message could be an innocent selfie, it could also be a company-classified plan.

4. Becoming defensive or secretive about work

A person becoming secretive or evasive about what they are working on should be an alarm bell. Corporate spies may have to create business reports or presentations for their other employer, and will need to do additional work for this role to be plausible. If you notice such evasion, take action quickly and ask questions. (Try not to be a micromanager in the process, however, and avoid making direct accusations, but instead use a coaching approach.)

Related: Learn How to Protect your Business and Others From Cyber Attacks

5. Equipment or files go missing

Espionage can be hard to detect, but missing equipment and/or files are two of the most common clues. You may not suspect anything at first, but over time might notice that staff members may be vague about what’s going on with business plans and projects. There may also be absences that coincide with such disappearances. More than one laptop stolen or otherwise “just vanished without a trace” should raise flags.

6. Unexplained drops in sales or profits

Business owners know that sales dips are signs that something is wrong. While there can be many reasons for a sudden drop, corporate espionage is certainly one. When business is slow, it’s natural for staff to try and find out what the problem is. If they’re not getting answers from managers, they may start looking into it themselves, and that’s when they may discover the corporate espionage taking place.

7. Employees quitting suddenly

Sudden resignations merit concern. If someone quits unexpectedly and without any apparent reason, it could be a sign that they’re leaving because their “mission” is complete. If you notice that someone has resigned abruptly, ask why. (Exit interviews are an effective tool.) Remember that such departures can also result from your working environment or culture, so be mindful of both that possibility and of the office environment as a whole.

Related: 7 Ways for Leaders to Gracefully Accept a Resignation

8. Accessing computer files without permission

Unauthorized computer access could mean that a person is trying to get hold of sensitive information. If you suspect that someone is accessing files without permission, investigate further: Check the logs to see which files have been accessed and by whom, monitor cloud files and be sure that all sensitive files have proper permissions structure. (Work with your cloud provider to make sure you understand such roles and permissions.)

9. Corporate secrets leaked to the press

If the media suddenly has access to confidential information, espionage is certainly a possibility. If you think your company’s secrets have been leaked, you should tighten security as well as investigate further. You can do both by looking for patterns in the leaks, as well as determining who may have had access to the information and how they may have obtained it.