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Avast Free Antivirus 2020 boot-time scan

Avast Free Antivirus 2020 Boot-time scan is a quite effective way of removing rootkits and other persistent 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.

Scheduling and dismissing an Avast Free Antivirus 2020 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.

Avast Free Antivirus 2020 system tray icon right-click menu, choose ‘Open Avast user interface’.

Open the Protection tab from the left side of the window and choose Virus Scans.

Avast Free Antivirus 2020, Protection. Click ‘Virus Scans’.

Click or touch the Open now button in the Boot-Time Scan section on the bottom of the window.

Avast Free Antivirus 2020, Protection, Virus Scans. Click ‘Open now’ for Boot-Time Scan.

Start by downloading the specialized database for boot-time scanning: click or touch the Install definitions link and wait until the process completes.

Avast Free Antivirus 2020, Virus Scans, Boot-time scan. Click ‘Install definitions’.

Next, verify that the Boot-time scan parameters are at their best: click the cogwheel icon on the top right of the Avast window.

Avast Free Antivirus 2020, Virus Scans, Boot-time scan. Click the cogwheel icon on the top right for scan settings.

If you protected Avast Free Antivirus settings with a password (recommended!), enter it now.

Avast Free Antivirus 2020, Authorization. Type the Avast password and click ‘OK, enter’.

By default, almost all Boot-Time Scan parameters in Avast Free Antivirus 2020 are fine. The only one you need to modify is in the Scan areas section – set this to All Harddisks.
Click or tap the red X button on the top left to close the Settings window.

Avast Free Antivirus 2020 settings, Boot-Time Scan. Set Scan areas to ‘All Harddisks’ and close the window.

Continue by clicking the Run on next PC reboot button. This will schedule the Boot-time scan for the next system restart, but please note that the scan will not start yet!

Avast Free Antivirus 2020, Virus Scans, Boot-time scan. Click ‘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 or tap the Cancel scheduled scan link instead.

Avast Free Antivirus 2020, Virus Scans, Boot-time scan. Click ‘Cancel scheduled scan’ to dismiss the boot-time scan.

Boot-time scanning with Avast Free Antivirus 2020

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 the 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.

Avast Free Antivirus 2020, Boot-time scan complete.

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

Checking Avast Free Antivirus 2020 Boot-time scan history

As Windows usually launches right after the Boot-time scan completes, you might want to check the log later.

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

Avast Free Antivirus 2020, Protection, Virus Scans. Click ‘ Scan history’.

A list of completed scans appears, click the arrowhead down button to the right of the correct scan log to see more information on scanned and detected/removed items.

Avast Free Antivirus 2020, Protection, Virus Scans, Scan history

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, 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).
    You can also use either System Repair Disc (Windows 7) or Recovery Drive (Windows 8.1 and 10) for booting your device.
    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?). Please see the Restore a System Image article for instructions.
    No backups? Use Puppy Linux for rescuing your files and reinstall Windows.

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