For NAS you need to use Symantec AntiVirus for Network Attached Storage
Symantec AntiVirus for Network Attached Storage (NAS) provides scalable, high-performance virus scanning and repair services to protect valuable data stored on network-attached storage devices. The solution provides increased scanning performance and improved detection capabilities for protection against multi-blended threats. NAS employs Symantec antivirus technologies using Symantec Scan Engine to detect viruses, worms, and Trojan horses in all major file types, including mobile code and compressed-file formats. Virus definitions and engines are updated automatically with no interruption in virus scanning using Symantec LiveUpdate.
http://www.symantec.com/business/antivirus-for-network-attached-storage