How do I manually update virus definitions without an internet connection?

Details

This article guides you through updating virus definitions using a computer if you are unable to update the virus definitions using the methods in this article.

Environment

You are using a PC with an internet connection.
Your NAS is running DSM 6.0 or above.

Notes:

You cannot update virus definitions for Antivirus Essential on DSM 5.2 and below because the ClamAV version used on that DSM version is no longer supported. (Learn more)

Resolution

Download the the following 3 definition files using a web browser on your computer:¹

http://database.clamav.net/daily.cvd
http://database.clamav.net/main.cvd
http://database.clamav.net/bytecode.cvd

Put the definition files in a shared folder (e.g., "Downloads") on your Synology NAS via File Station.
Sign in to your Synology NAS via SSH and switch to root permission. Refer to this article for instructions.
Enter the following commands one by one. Make sure to replace volume1 and Downloads with the volume and shared folder in which your files are located.

cd /var/packages/AntiVirus/target/engine/clamav/var/lib

rm *.cvd

mv /volume1/Downloads/*.cvd .
The virus definitions are now updated. You can view the virus definition’s release date at Antivirus Essential > Update.²

Notes:

If you are unable to download these files, try using a PC with a different public IP address and download them again. Please refer to ClamAV's official documentation for more information.
The status page will remain as Update check failed as long as there is no internet connection.

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