Bypass the updater:
Re: Antivirus sofware on a Mac...
You DO NOT (under ANY circumstances) need Antivirus software on a Mac and in most every case, having it will cause more problems than it will ever solve.
At this time there have been no confirmed Mac OS X viruses (subject to the semantic debate about whether the old iChat exploit, now long since blocked, was properly classified as a virus or a trojan horse, and not counting the Word macro virus that can affect Office v.X or non-updated copies of Office 2004) and very few trojan-horse programs. I therefore do not feel that antivirus or antispyware software is necessary at this time as long as users are careful about what they download from the Internet or accept as attachments via email and keep their systems updated with the latest patches from Apple.
The most common exploit is an outbreak of "scareware" that people are encountering while web surfing. This "scareware" pops up and claims that your system is infected with viruses, prompts you to download their "scanner", then tells you that you need to purchase their paid software to remove them. These fake applications, appearing by many names including Mac Defender, Apple Security Center, Apple Web Security, and many others, do nothing at all other than turn off the fake warnings once they have your money. DO NOT fall for these. There was also a recent trojan that used a flaw in Java, now patched, but if you didn't have Java turned on (recommended if you don't use Java-based sites regularly), it wouldn't have affected you.
Security precautions for Mac OS X mostly are common sense: don't download and run files from sites you don't know, don't fall for any "you have viruses" messages, don't double-click on attachments in emails you aren't expecting and/or from people you don't know, and make sure you password your system with a non-trivial password and keep that password secure. In addition, don't leave your system available in a public place and unattended where someone unauthorized could use it and potentially install malware (such a policy is also a precaution against theft). Also be sure to keep your system and applications patched with all current security updates.
It is possible for a Mac user to inadvertently forward a Windows virus to a PC user though you'd have to do it manually so the above precautions would probably prevent such virus-spreading, and said Windows virus cannot infect the Mac.
If you do decide you wish to run antivirus software, I think that the donationware clamXav should be more than enough, but it is ENTIRELY UNNECESSARY.
If you're running Windows on your system, either via BootCamp, Parallels Workstation or another solution, then that copy of Windows is subject to all the myriad exploits common to the Windows world, so you need to take full precautions, including running both antivirus and antispyware software ON THE WINDOWS PARTITION. If you don't run Boot Camp, you'll never need it.
Tha same reason you get a "could not find a program to run this file" message with the "exe" file (a Windows only file), is the reason that viruses don't affect Mac OS. It's a Unix based BSD, and "exe" files have nothing that can open or run them.
My apologies--they're actually .dmg files.
DMGs open with the DiskImageMounter app (Mac HD/System/Library/Core Services is where to locate it)
If you see the "cannot find" error, right click the DMG and "Get Info"
Under "Open with", click the drop down and browse to the aforementioned location to select the app.
Worst case, download this zip file (Install Flash Player OS X).
Extract it using Stuffit Expander and double click it. No DMG, just the installer.