If you suspect that your PC contains malware, Avast Antivirus allows you to schedule a Boot-Time Scan to run the next time your computer starts. It scans for known types of malware and removes threats before the operating system and other services boot up.

Boot-Time Scan is an advanced feature designed to use when you suspect a threat in the system, and usually takes some time to complete. It does not run automatically or on a regular basis — you need to manually schedule the scan when you need it.

Before scheduling and running a Boot-Time Scan, you need to specify how Boot-Time Scan responds to detected threats. This article also contains information about general Boot-Time Scan settings, which allow you to specify scan sensitivity, and what issue types are detected by Boot-Time Scan.

Manage threat responses

To specify which action(s) Boot-Time Scan applies when it detects a threat, you need to manage automatic actions. When you use automatic actions, Boot-Time Scan applies the specified actions automatically. Alternatively, when you disable automatic actions, you are prompted during the Boot-Time Scan to manually select an action for each detected threat.

To specify how Boot-Time Scan responds to detected threats:

1. Open Avast Antivirus and select Protection ▸ Virus Scans.
2. Click Settings (the gear icon) on the right side of the screen.
3. Select the Boot-Time Scan tab.
4. Scroll down to Perform automatic actions during this scan. Tick this option to enable automatic actions, or untick it to disable automatic actions. If you leave this option unticked, Avast asks you what to do each time a threat is detected during the Boot-Time Scan.
5. If you enabled automatic actions in the previous step, select your preferred automatic action:
   • Fix automatically (recommended): Avast Antivirus attempts to repair the file. If unsuccessful, it moves the file to Quarantine or deletes the file if neither action is successful.
   • Move file to Quarantine: Avast Antivirus sends the file to Quarantine, where it cannot harm your system.
   • Delete file: Avast Antivirus permanently removes the file from your PC.
   

When you run Boot-Time Scan, Avast Antivirus responds to detected threats according to your preferences.

Run Boot-Time Scan

After specifying how Boot-Time Scan will respond to detected threats, follow the instructions below to schedule it:

1. Open Avast Antivirus and select Protection ▸ Virus Scans.
2. Click the Boot-Time Scan tile.
3. Click Install definitions, then click Run on next PC reboot to run the scan during the next system restart.

4. Restart your PC. When the system restarts, a Boot-Time Scan progress screen appears.
5. For any detected threat, Avast Antivirus applies the action specified in your application settings. If automatic actions are enabled, Avast Antivirus resolves detected issues without any actions required from you. If you disabled automatic actions and a threat is detected, follow the on-screen instructions to manually select which action Avast Antivirus applies.

The scan usually takes several minutes, but the duration varies depending on the speed of your system and the number of files being scanned. When the scan is complete or skipped, Windows continues booting up.

Adjust scan settings

1. Open Avast Antivirus and select Protection ▸ Virus Scans.
2. Click Settings (the gear icon) on the right side of the screen.
3. Select the Boot-Time Scan tab.
4. Define the following settings for your next Boot-Time Scan:
   1. Sensitivity: use the slider to indicate your preferred level of heuristic sensitivity. Heuristics enable Avast Antivirus to detect unknown malware by analyzing code for commands that may indicate malicious intent.
   2. Scan for PUPs (potentially unwanted programs): ensure this box is ticked if you want Boot-Time Scan to look for programs that are stealthily downloaded with other programs and typically perform unwanted activity.
   3. Unpack archive files: ensure this box is ticked if you want Avast Antivirus to unpack compressed files during the scan.
   4. Scan areas: select All Harddisks or System drive to specify which data space you want the scan to analyze.
   5. Auto start programs: allows Avast Antivirus to scan programs that automatically start when you turn on your computer.
   6. Automatic actions: configure automatic actions for any threats detected by Boot-Time Scan.