I first wish to thank /u/ElementalPee for providing the critical information I needed to successfully update Clam Antivirus for Linux Mint (64 bit Cinnamon 18,1 S) ; this renders my previous issue essentially resolved.
This second problem is relatively minor, yet relates to how I solved the first. After several interruptions due to a spotty Internet connexion, the necessary files (to wit main.cvd, daily.cvd and bytecode.cvd) were all successfully downloaded and updated. However, the following message appeared finally before the command prompt:
WARNING: Clamd was NOT notified: Can't connect to clamd through /var/run/clamav/clamd.ctl: No such file or directory
Surely enough, when I open Clamtd (the GUI for Clam Antivirus), the light yellow bar Eine Aktualisierung ist verfügbar [an update is available] appears along the bottom. Running sudo freshclam confirms that my virus signatures are indeed up to date. I would rather cause this erroneous message to disappear, that I may properly set up automatic updating later. Of the files available from the Packet Manager that include clam in their titles, I have Clamtk, Clamav-base, Clamav-freshclam, Libclamav7 and Clamav. How may I rectify this?