Q: Can anybody give me advice on"Viruses and the like.

Stop wasting your time with them. They usually cause more problems than they can hope to prevent.

See Thomas' Mac Malware Guide: http://www.thesafemac.com/mmg/

Server.app has clam installed, alternatively you can install ClamXav from the App Store, but you have to use it manually.  I download ClamXav from clamxav.com - then you can have ClamXavSentry installed and just have it monitor your Download folder or other subfolders in your home directory.  I just have it set to watch my Desktop for things I drag from a browser window and drop on my desktop and the ~/Downloads directory.

In any event, don't pay for an anti-virus program, find a free one if you think you need it.  I think you can get a free one from Sophos (but last I checked it was a resource hog) and maybe a couple of other places, but I would stick with clam, it's what Apple uses with the 10.7 and 10.8 server apps.

Security Steps and Behavior

Harden your Mac against malware attacks

Security Issues Warning List

Uninstall all your installed anti-virus softwares according to the developers directions.

Install the free ClamXav here if you are dealing with Windows files, run as you need it.

http://www.clamxav.com/

Else all you need to do is watch that your not being tricked into installing something.

Actually, the clamscan virus defintition databases have been including signatures for os x directed trojans and malware for several years now, at least since Tiger.

That being said, Apple has indeed included it's XProtect version since about 2009, that's why if you do a verbose boot, you'll see something like:

Quarantine policy loaded.