Leopard update (11/1/07) — There are problems running Live Update under Norton/Symantec 10.1 from Essential Software. An update is expected soon.

Mac Hunting Season Open? (11/2/07) Wired  is reporting a new trojan than can attack Macs. The article is here. As usual, the initial reception outside of companies that write (or would like to write) security software for the Mac platform is cool. Time will tell whether this one has any credibility. In the past, these have been quietly dismissed. 

Stanford provides Norton Anti-Virus on http://ess.stanford.edu 

The auto protect mode tends to degrade computer performance, although this is less noticeable on the newer machines. It's a good idea to run a Norton scan at least weekly, or any time you are suspect of any virus exposure. It's still possible to receive and unknowingly pass on a virus to a Windows user. If you scan your entire hard drive, it may take a while; so doing this during idle time, or overnight, will less disruptive to your workflow.

With the Intel Macs, running Windows (with Boot Camp or Parallels), the same protection is needed as with any Windows system. The same is true for the older Virtual PC on PowerPC (non-Intel) Macs.