Vulnerability blocked: OS X Apple File Print Remote BO

In the last two days I keep getting this popup from Norton Internet Security 5 v.5.10 (33) on my Mac running maxOS Sierra 10.12:

"Vulnerability blocked: OS X Apple File Print Remote BO" - it shows an IP address where the attack is coming from, and it turns out that IP address is my Synology NAS.  I have turned off remote access on my NAS, but am still getting this notification.

Does anyone know what might be causing this?

Thanks,

Peter