Since DSM 4.1 you can configure proxy service at the Control Panel – Network:

but if you have installed the AntiVirus Essential package, it wouldn’t use this settings to update it’s virus definitions and will fail:

To configure autoupdate for the virus definitions behind a proxy server, you need to configure some settings manualy:

activate ssh on your NAS:

connect to your NAS by SSH and login as root (not as admin!)

create a new script:

vi /var/packages/AntiVirus/target/bin/synoavupdate

change vi to the insert mode by press key i, then insert this lines:

#!/bin/sh
cd /var/packages/AntiVirus/target/engine/clamav/var/lib
rm daily.cvd
export http_proxy="proxy.test.local:8080"
wget http://database.clamav.net/daily.cvd --proxy=on

to change vi to the command mode press ESC key. Save your script by enter :w and leave vi by enter :q.

now you need to make your new script executable:

chmod +x /var/packages/AntiVirus/target/bin/synoavupdate

you can test your script by entering:

/var/packages/AntiVirus/target/bin/synoavupdate

After executing your script, your AV definitions should be uptodate:

To execute your script automaticaly on a reglar base, edit /etc/crontab:

vi /etc/crontab

add the follow lines to the crontab file and save it:

#minute hour    mday    month   wday    who     command
0       0       *       *       6       root    /var/packages/AntiVirus/target/bin/synoavupdate
0       1       *       *       6       root    /var/packages/AntiVirus/target/bin/synoavscan --all

edit the times, so that synoavupdate runs around one hour before synoavscan.

Deactivate automatically updates in your settings:

Don’t forget to deactivate SSH access again.