Avast Free Antivirus 2019 boot-time scan

The latest available version is Avast Free Antivirus 2020, the same article is available as Avast Free Antivirus 2020 boot-time scan.

Avast Free Antivirus 2019 Boot-Time Scan is a more effective way of removing rootkits and other sneaky malware because the scan takes place before Windows starts up and therefore rootkits and other system modifiers have less chance of hiding themselves.

However, there are some important caveats:

  • inexperienced users can easily make Windows unbootable if they allow Avast to delete or move system files,
  • boot-time scanning takes a long time – up to several hours.

It is strongly recommended to create a System Repair Disc (Windows 7) or Recovery Drive (Windows 8.1 and 10) and a System Restore point before running the Boot-time scan, and a full backup of your device is even better.

Quick overview video of Avast Boot-Time Scan

Here is a short video about boot-time scanning with Avast Free Antivirus 2019. More details are provided below.

Scheduling and dismissing an Avast Free Antivirus 2019 Boot-Time Scan

Open Avast user interface (aka the main window) by clicking its yellow/orange icon in the Taskbar Notification area (aka System Tray), or by opening Avast from Start menu or Start screen. It is also recommended to save all open documents and close all running programs and apps.

Click Protection on the left side of the window and choose Virus Scans.

Avast Free Antivirus 2019, Protection, Virus Scans

First, verify that the Boot-Time Scan parameters are at their best: click the Settings link below the Boot-Time Scan button.

Avast Free Antivirus 2019, boot-time scan settings

Here is the screenshot of recommended Boot-Time Scan parameters: all hard disks and start-up programs are fully scanned, plus Avast looks for potentially unwanted programs and checks within archive files. All threats are fixed automatically unless the infected files are in important system folders.
Click or tap the red X button on the top left to close the Settings window.

Avast Free Antivirus 2019, default settings for boot-time scans

Avast Free Antivirus offers to download specialized definitions for better rootkit detection before a Boot-Time Scan. This is important, so please click or tap the Install specialized definitions link.

Avast Free Antivirus 2019, install specialized definitions

After the definitions have been installed, click Run on next PC reboot. This will schedule the Boot-Time Scan for the next system restart. Please note that the scan will not start yet!

Avast Free Antivirus 2019, run on next PC reboot

Make sure all other programs, apps, and documents are closed, then restart your device yourself.

To discard the Boot-Time Scan, click Cancel scheduled scan instead.

Avast Free Antivirus 2019, cancel the scheduled scan

Boot-time scanning with Avast Free Antivirus 2019

You can stop a Boot-Time Scan at any time by pressing the Esc key on your keyboard, but I do not recommend doing this unless you need to: your computer might still be infected and you should reschedule the scan to clean the PC.

This is how the Avast Boot-Time Scan looks like. All infected files that are not in important system folders (for example, C:\Windows\) are automatically moved to Virus Chest (aka Quarantine).

Avast Free Antivirus, boot-time scan running

In case Avast detects an infected system file that is critical for running Windows or is located in the Windows folder or its subfolders, it stops and waits for an action to perform. In such cases, press number 3 on the keyboard to skip moving the file.
If you are an expert and you know that the file in question is not required by Microsoft Windows, you can use option 1 to move the infected item to Chest.

Do not use the Yes or Yes all options for system files – your computer might become unstable or unbootable!

Avast Free Antivirus, Boot-time scan, File is in Windows folder. Choose option 3.

If Avast boot-time scan detects corrupted files, it warns about these (for example, the Archive is corrupted message), but no action is taken. This is usually related to incomplete downloads in the Downloads folder, but it could also indicate file system errors. In the latter case, please see the Check disks in Windows tutorial for instructions on how to scan and fix drives.

As said before, the scanning might take up to several hours. After the long process is complete, an overview of the results is displayed for a few seconds and Windows will start.

If Windows has trouble starting or crashes after the boot-time scan, scroll down to the last section for solutions.

Checking Avast Boot-Time Scan history

As Windows usually starts right after Avast Boot-Time Scan completes, you might want to check the log later. This option was gone in Avast Free Antivirus 2018 but returned with version 2019.

To see Avast logs, open the Protection tab and choose Virus Scans. Then click or tap the Scan history link on the top right.

Avast Free Antivirus 2019, Scan history

A list of completed scans appears, click the Details link to see more information on scanned and detected/removed items.
After checking the logs, close the window using the red X button on the top left.

Avast Free Antivirus 2019, scan history details

Troubleshooting if Windows does not work properly after Avast Boot-Time Scan

In case you experience problems with starting or running Windows after a boot-time scan, you can follow these steps to get your PC running properly again:

  • If Desktop is empty and no Taskbar appears after signing in, use keyboard shortcut Ctrl+Shift+Esc to launch Task Manager, open File menu and click New Task (Run). Type explorer and click OK. Desktop icons and Taskbar should appear now. If not, continue to next steps.
  • Start Windows in Safe Mode, then open Command Prompt and run sfc /scannow. This will restore essential system files.
  • If launching Windows in Safe Mode is not possible, Windows 7, 8/8.1 and 10 users can boot from installation DVD or USB stick and click Repair your computer (see the Repair your computer in Windows Vista or 7, Repair your computer in Windows 8 and 8.1 or Repair your computer in Windows 10 article for more detailed instructions).
    Windows 7 users can also use System Repair Disc for booting; Windows 8/8.1 and 10 users can use Recovery Drive for the same task.
    Try Startup Repair/Automatic Repair first. If this is of no help, see other options in the linked tutorials above.
  • If repair options are not helping, restore Windows from the latest backup (you do have one?). Windows 7, 8/8.1 and 10 users can see the Restore a System Image article for instructions.
    No backups? Use Puppy Linux for rescuing your files and reinstall Windows.

More Avast Free Antivirus 2019 tutorials

As long as you are using Avast as your main security tool for Windows, please see these guides for better protection and performance. Please do note that the latest version available is Avast Free Antivirus 2020.