Ah, I've had that one before. I did a quick search online and found this:
"From the main page of NSS, select Settings > Antivirus > Scan & Risks tab and then under Items to Exclude from Auto-protect and Sonar Detection, click on the Configure(+) , then click on ADD and on the Add Item screen, click on the Folder and browse to the folder you desire to exclude, highlight it, Apply and OK out."
Please do let me know if that helps!