'Scan this Mac' does not scan network shares which are not mounted in /Volumes/.
Sophos product and version
Sophos Anti-Virus for Mac OS X
What to do
You can scan network shares in any of the following ways:
- create a custom scan and add the volumes to that scan
- locate them in the Finder and select 'Scan with Sophos Anti-Virus'
- drag them to the Sophos Anti-Virus dock icon
'Scan this Mac' is designed only to scan local (i.e. not network) volumes. It does not scan network shares which are not mounted in /Volumes/.
The above methods are used for scanning network volumes.