You do not need a subscription to an antivirus product to scan your Windows computer for malicious files.  Windows 10 and Windows 11 both have an antivirus scanner built into Windows Security . 

WINDOWS SECURITY 

You can launch the Windows Security app by Start -> Settings -> Update & Security -> Windows Security and select the button “Open Windows Security settings“. 

Once Windows Security app loads, select Virus & threat protection.  

From the Current threats section, you can review information regarding previous scan and run a Quick scan. 

Select Scan Options to customise your scan or to scan a specific folder or drive. 

Select Full scan to scan all the folders and files on the computer. This scan can take upwards of an hour depending on how much data is on your drive. 

Select Custom scan to restrict the scan to a specific set of folders or to select a different drive or attached drive, such as a USB stick. 

Select Microsoft Defender Offline Scan to scan and remove threats that the Full scan fails to remove. You will need to save ad close your work as this option will restart your system in “Offline” state. Once the scan completed, the computer will reboot into Windows. 

Before you run a scan you can make sure you are scanning for the most recent known threats by selecting Check for updates. 

After the scan completes, you can check if any malicious files were detected in the Protection history.