Fix Avast Service High CPU Usage

If Avast’s background service is using high CPU, the fix is usually to disable a few resource-heavy shields, update the program, or run a full scan to rule out malware. This article explains the common causes and provides step-by-step fixes you can try in order, from quickest to most thorough.

Why Avast Service Uses High CPU

Avast runs several background processes that scan files, monitor network traffic, and check for suspicious behavior. The main service, avast! Antivirus (shown as AvastSvc.exe in Task Manager), can spike in CPU usage for a number of reasons:

• An outdated virus definitions database that causes constant rescans.
• Conflicts with other security software (even a previously installed antivirus can leave drivers behind).
• A corrupted installation or a failed update.
• Heavy disk activity from a scheduled scan running at an inconvenient time.
• Malware that is actively trying to hide from the antivirus, causing repeated scans.

Sometimes the high usage is temporary, such as during a full scan or after a major update. But if it persists for hours or days, one of the fixes below should help.

Quick Fixes to Try First

Start with these simple steps—they resolve many cases without changing how Avast protects you.

1. Restart your computer. This clears temporary glitches and stops any stuck scan process.
2. Update Avast. Open the Avast interface, go to Menu (three horizontal lines) > Settings > Update and click Check for updates. Install both program and virus definition updates, then restart.
3. Run a full scan. A quick scan may miss malware that is causing the high CPU. Go to Protection > Virus Scans > Full Virus Scan. Let it finish; it can take an hour or more.
4. Check for other security software. If you have another antivirus (even a free one) or a firewall that isn’t Windows Defender, uninstall it or disable its real-time protection. Conflicting drivers often cause Avast to work harder.

Disable Resource-Heavy Shields

Avast has several real-time shields that protect different parts of your system. Disabling the ones you don’t need can dramatically reduce CPU usage without leaving you completely unprotected.

1. Open Avast and go to Protection > Core Shields.
2. You’ll see toggles for File Shield, Web Shield, Mail Shield, and Behavior Shield.
3. Turn off the ones you don’t use. For example, if you don’t use a desktop email client (like Outlook or Thunderbird), you can safely turn off Mail Shield.
4. If you’re on a trusted network, you can also turn off Web Shield temporarily to see if CPU drops. Re-enable it when you’re on public Wi-Fi.

Keep File Shield on—it’s the core protection. If you disable all shields, you’ll see a warning that your system is unprotected, which is not recommended.

Adjust Scan and Update Settings

Avast’s default settings may cause scans to start when you’re working, or updates to happen too frequently. Changing these can reduce background CPU spikes.

• Schedule scans for idle time. Go to Protection > Virus Scans > Schedule and set the full scan to run at night or when you’re away from the computer.
• Reduce update frequency. In Settings > Update, you can change the virus definitions update interval to every 4 hours instead of every hour. This cuts down on background network and disk activity.
• Disable “Scan on file execution”. In File Shield settings, you can uncheck “Scan on file execution” to avoid scanning every time you open a program. This is a trade-off—you lose some protection, but CPU usage drops significantly.

Repair or Reinstall Avast

If the above steps don’t help, the installation may be corrupted. A repair is easy and keeps your settings.

1. Open Control Panel > Programs and Features (or Settings > Apps on Windows 10/11).
2. Find Avast Free Antivirus (or your version), click it, and select Repair.
3. Follow the prompts and restart your computer.

If the repair doesn’t work, uninstall Avast completely using the official Avast Uninstall Utility (available from Avast’s website) and then reinstall the latest version. This removes all leftover drivers and settings.

When to Consider Switching Antivirus

If you’ve tried everything and Avast still uses 50-100% CPU constantly, it may be incompatible with your hardware or other software. Some older PCs simply don’t handle Avast’s resource usage well. In that case, you might switch to a lighter antivirus like Windows Defender (built into Windows) or another well-known free option. Windows Defender is actually quite good and uses fewer resources on most systems. If you do switch, make sure to uninstall Avast completely to avoid conflicts.

Frequently Asked Questions

Is it safe to disable Avast shields?

Disabling individual shields temporarily is safe if you’re careful. You lose that layer of protection, but you can re-enable it later. For example, turning off Mail Shield when you don’t use a desktop email client is fine. Turning off all shields leaves you vulnerable, so only do that for troubleshooting and re-enable them immediately after.

Why does Avast use CPU even when I’m not doing anything?

Avast runs background processes constantly to check for threats. Scheduled scans, updates, and background checks can all cause CPU spikes even when you’re idle. If it’s constant, it’s usually a sign of a conflict or a corrupted installation.

Will uninstalling Avast remove all its files?

Regular uninstall may leave behind drivers and registry entries. That’s why Avast provides a special uninstall utility that removes everything. Use that if you plan to switch or reinstall.

Can Avast slow down my computer even if CPU usage is low?

Yes, Avast can also cause high disk usage or memory usage, which slows down your system. The same fixes for high CPU often help with disk and memory issues. If you notice your hard drive is constantly at 100%, check if Avast is the cause in Task Manager.

Does Avast have a gaming mode to reduce CPU usage?

Yes, Avast has a “Do Not Disturb” mode that suppresses notifications and pauses background scans when you’re in full-screen apps or games. You can enable it in Settings > General > Do Not Disturb. It helps, but it won’t fix a persistent CPU issue.

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