Hey there! Let me walk you through answers to your questions based on my experience and what I've seen in the Ubuntu/Linux community:

How effective is ClamAV? #

ClamAV is a reliable open-source option for signature-based malware detection—meaning it catches known threats by matching their code patterns. It’s particularly useful if you’re scanning files to share with Windows systems, since it covers a huge library of Windows malware signatures. That said, it’s not the best at detecting Linux-specific malware or zero-day threats (new, unrecorded malware).

Your 4-hour scan time is totally normal for a full system scan. If you want to speed it up, you can exclude non-critical directories (like ~/Downloads if you trust those files) using the --exclude flag in the command line, for example:

clamscan -r / --exclude=/home/yourusername/Downloads

Are those "viruses" likely false positives? #

Absolutely—false positives are super common with ClamAV on Linux. It often flags legitimate custom scripts, self-compiled binaries, or even some system files because they match generic malware signatures.

To confirm, pull up the specific file paths from your logs and cross-check them against what you know about your system. If it’s flagging a script you wrote or an app you installed from a trusted source, it’s almost certainly a false positive. You can whitelist these files by adding their paths or hashes to ClamAV’s whitelist.ign2 file, then restart the ClamAV service to apply the changes.

Better alternatives for system integrity checks? #

Here are some solid options to complement or replace ClamAV:

• rkhunter & chkrootkit: These are specialized rootkit detectors. They scan for hidden processes, modified system binaries, and suspicious configs. Run them with sudo rkhunter --check or sudo chkrootkit—just note they can also have false positives, so verify any alerts.
• Sophos Antivirus for Linux: A free commercial tool with stronger detection for Linux-specific threats and fewer false positives than ClamAV. It’s also lighter on system resources.
• debsums: If you want to verify that your Ubuntu system packages haven’t been tampered with, this tool is perfect. Install it with sudo apt install debsums, then run sudo debsums -c to see any modified files from official packages.
• Tripwire: An advanced integrity monitor that creates a baseline of your system files and alerts you to any changes. Great for long-term monitoring, though it requires some setup to whitelist expected changes (like system updates).

Final thought #

ClamAV works well for basic scanning, but pairing it with rootkit tools and system integrity checkers will give you a much more complete view of your PC’s security. Don’t panic about the "many viruses"—most are likely false positives, so take time to investigate each one.

备注：内容来源于stack exchange，提问作者ilie alexandru