How to Run a Defender ATP (Windows Security) Scan on a PC Step 1 Click the search icon on the bottom left and search for Windows Security. Step 2 Click Open to open the Windows Security (Defender ATP) application. Step 3 Click Virus & Threat Protection from the left-side menu. Step 4 You will be taken to the Scanning screen. If you would like to initiate a manual quick scan, click the Quick Scan button. Step 5 To conduct a full scan, click Scan options under the Quick scan button. Last modified: September 25, 2020