Assuming you are using Windows Defender which is the anti-virus solution built in Windows 10, you may not know that it has an offline scan feature that lets you scan your Windows 10 system during boot time without internet connection.
Here is how you can launch it if you feel the need to scan your computer to make sure it’s clean.
Go to Settings app → Update & Security → Windows Defender, scroll down a bit until you see Windows Defender Offline.
And click Scan Offline to start the process within a minute after the message “Computer will start within a minute” pops up. The computer reboots and launches Windows Defender to do a full system scan before starting in Windows 10.
This new scan offline feature is part of Windows 10 build 14271 which is currently released to Fast Ring users only at the moment.
Windows Defender Offline is nothing new and has been around back in 2011. It’s a standalone program that you can download and run on your system to scan the PC during the boot process. Check this post for more details if you are still on Windows 7 or 8.1.