No. Antivirus can detect and block many threats, but no scan can prove that a device is malware-free. A threat may be new, concealed, altered to evade detection, or able to interfere with security software. Keep antivirus enabled and updated, but treat it as one layer of protection—not a guarantee.
Can antivirus miss malware?
Yes. Antivirus tools use methods such as known-threat signatures and behavior-based detection. Using both can improve coverage, but neither method catches everything. CISA recommends current signature- and behavior-based detection and quarantine of malicious files; that guidance does not promise perfect detection.
Some malware is designed to evade security tools. CISA’s April 9, 2015 AAEH malware alert documented malware that could block connections to security-company IP addresses and prevent antivirus tools from running on infected machines. This is a documented example, not evidence of how common that behavior is today.
Other threats conceal code, disable defenses, or use legitimate system utilities to blend in with ordinary activity. CISA’s May 24, 2023 advisory describes actors using built-in tools to avoid some endpoint detection alerts. That is why a scan that reports no detection is not the same as confirmation that a device is clean.
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What does a clean antivirus scan tell you?
It tells you that the scan did not identify malware with the tools, definitions, settings, and files it checked at that time. It does not rule out a threat the product did not recognize, a threat that avoided the scan, or a problem that prevented the security software from working properly. CISA describes antivirus as protection against “most known viruses,” not all possible infections.
There is no universal antivirus detection percentage that can establish whether every product or scan will find every infection. Product comparisons depend on factors such as test date, methodology, operating-system coverage, and whether testing measures real-time or on-demand scanning.
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What to do if you are worried about an infection
Check the protection you already have
- Keep your operating system, applications, antivirus, and detection updates current. CISA recommends maintaining antivirus definitions and installing software patches.
- Confirm that real-time protection is enabled, and review alerts and scan results rather than assuming the product is configured correctly.
- Do not open a suspicious attachment or run an unexpected download just because a scan found nothing.
Get help when the risk remains
If you still suspect a compromise, follow the official security guidance for your device’s operating system or seek qualified support. The right response depends on the device, symptoms, and whether accounts or work systems may also be affected; avoid deleting suspicious files or continuing to use a potentially compromised device without context.
For organizations, add monitoring and response
Organizations should layer endpoint protection with review of scan results and alerts, and consider endpoint detection and response (EDR) for greater visibility. CISA’s AA22-137A guidance recommends anti-malware on workstations, routine review of scan results, and endpoint detection tools. During ransomware investigations, CISA’s #StopRansomware Guide also discusses examining detection systems and logs.
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How backups fit into malware protection
Backups help you recover files if an incident causes loss or encryption; they do not detect or remove malware. Keep backups separate from everyday use where practical, and check that you can restore them. CISA’s ransomware guidance covers recovery planning, while its election-security toolkit describes external-drive backups as one option.
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