Defense: Malware targeting Mac's

Question

Mac's users running any browser with JavaScript turned on by default are vulnerable to being tricked into clicking on a trick image and/or link.
That image may appear to be a standard OS X window with a close box or the typical OS X looking window asking a question with OK or Cancel. It can look like anything really, it's purpose is designed to get you to click anywhere on it and initiate a download to your computer.
Safari tries to be helpful and "Open Safe Files" by default, which is being used with numerous success to run code on one's machine, by bypassing the normal user action of 'open the downloads folder and then clicks on the download to run' process in exchange for convenience.
Most Mac's are used with one person, and the initial setup of a new Mac (or a new OS X install) is the first user is automatically a Administrator User. Running one's typical day to day use while in Admin User mode gives any code running on one's machine more privileges and access than it would receive if the user of the computer created another OS X account and ran most of their computer use as a General User.
The ultimate access for rogue code would be Root User, which on Mac's is turned off by default, however a temporary access window to Root User is allowed when a Admin User provides his or her Admin Password. Once rogue code gets Root user access, it's all over, OS X is completely compromised.
The key to security on a Mac, or any computer system actually, is a process called "Compartmentalized Security" where the more privileges code receives, the more it's subjected to time and scrutiny to determine it's legitimacy.
Web browsers are the forward troops facing a overwhelming enemy, the World Wide Web. Not one modern web browser is 100% safe, not Safari, not Firefox, not IE, not Chrome, not Opera. Neither are plug-ins or scripts that run within these browsers 100% safe.
So the key to maintaining security is to provide a high level of "Compartmentalized Security" steps which shifts the exploit potential further down the privilege level so it can't do much of anything or gain further access.
People can get carried away with downloading and installing software in a rapid fire manner, this provides a ripe opportunity for malware to get onto one's computer, even gaining root access right away.
So in order to provide better compartmentalized security, provide more time and steps before potentially installing rouge code. I suggest the following actions:
1: Run most of your day to day computer use as a General User with less privileges. This can be done by creating a new Admin User, logging out of the present user and into the new Admin User, then turning the first user into a General User.
Whenever certain actions are needed, like accessing the Application's folder (where programs can be changed by malware) a Admin Name and Password will be required. A small hassle, but it provides another step for it to get past.
2: Use Firefox web browser and the following Add-ons: NoScript, Ad Block Plus and Public Fox.
Under the Toolbar customization, drag the NoScript button to the toolbar. NoScript turns off all scripts and plug-ins by default, which if you trust the site your on, you click the button for turning them on and the page automatically reloads.
In Public Fox preferences, set a password on downloads, this way a popup window appears before any download occurs, keeping malware from sneaking into your downloads folder and potentially being clicked on.
With Ad Block Plus, subscribe to the Easy List which automatically appears in the browser window. This will auto-update to keep advertising, which has been used numerous times as a attack venue, from appearing.
Click&Clean, Ghostery, BetterPrivacy, FlagFox, WOT, HTTPS-Everywhere (from the Electronic Frontier Foundation) are also highly recommended add-ons.
3: In Safari preferences, turn off "Open Safe Files" install the Ad Block Plus add-on and the Click2Flash add-on. If any add-on appears in the future to simulate what NoScript and Public Fox does on Firefox, then enable those add-ons.
4: Check the staus of your browser plug-ins. These websites makes it easy, bookmark them in a obvious place so you remember to visit them routinely. As soon as a vulnerability appears, either update or turn off the affected plug-in in your browser until a patch is issued.
https://www.mozilla.com/en-US/plugincheck/
https://browsercheck.qualys.com/
5: If you enjoy surfing the backalleys of the Internet and you have at least a decent dual core Intel based Mac, I'd highly advise installing the free VirtualBox and loading a free ISO of Linux Mint DVD 32 bit 10.10 (most consistent and easy to use, everything included, Linux distro)
http://www.virtualbox.org/
http://www.linuxmint.com/download.php
The object is to load and install Linux Mint into the virtual machine like installing a operating system onto a regular computer. Once completed, then save a snapshot to revert to after your Firefox browsing session (in Linux) is completed. All and any potential malware, caches etc is flushed when you revert the entire guest OS back to the earlier state. Keep the Guest OS updated via the Software Update option and save a new snapshot.
6: Use common sense, if it don't look right, then stop and flush the OS X based browser from memory via the Apple > Force Quit menu.
7: Install the free ClamXav, it will remove the OS X malware it knows about, offering some after the fact defense and Windows malware from their files.
http://www.clamxav.com/
I don't advise a full time, always on and running anti-virus solution for Mac's due to Apple's tendancy to change the underlining OS themselves to thwart potential malware. So something like Norton which maintains tight control over OS X should be avoided.
Malware on Mac's are a scarce thing because of Apple's top down approach, but trojans are a potential attack venue and people need to insure more steps to avoid being tricked.

Answer 1

Thomas A Reed wrote:
 That causes problems for some apps, which won't run on anything but an admin account or on the account they were installed on.
Then the programs need to be reinstalled for "All Users" which most do now by default or reinstalled for the new Admin account. Since the previously Admin is now a General User, it's not a issue. If the program needs Admin/Root access the user should be made aware of that fact and understand they just elevated privileges to a most dangerous level.
Linux has a security key that displays in the menu bar that one has opened a "sudo window" which any code run during that time can have Root level access. Of course OS X has no such warning.
And it's not a guarantee of security - a user who gets in the habit of authenticating to admin to install stuff from their Standard account is no safer than the user who gets in the habit of authenticating to install from their Admin account.  This is a good general suggestion, but may not work for everyone and provides practically no real security against "social engineering" by itself.
The only guaranty of security is unplugging the power from the computer and tossing the machine into a pit of molten lead.
The user is rarely installing/uninstalling or making such drastic changes to their machine that entering their Admin name/password is such a burden. Those rare folks who do reside in that realm or even for a short duration, log into the Admin User from the start and competent enough to know the difference anyway.
Again, using things like these won't protect you by themselves.  How do you know if a site is trusted and should have JavaScript turned on?  And most folks are finding this malware via trusted sites that have had malicious JavaScripts "sneaked" into their code, through malicious ads or search engine optimization poisoning.  How can you know if your trusted site is affected?  And, given how much this malware has been jumping around over the last week, I seriously doubt Ad Block Plus can keep up.
Well your LESS protected without them. So far the NoScript "web cop" Add-on has protected Firefox users from the MacDefender trojan by not allowing Javascript to run by default.
Even if a trusted site has the malware and one turns off NoScript for that site, then Public Fox (with a password block on downloads) stops any automatic download from occurring.
Ad Block Plus defends against advertising which has been used as a malware vector. It provides the option to whitelist  favorite sites which trust has been established by the user.
Again the reasoning here is to provide a "security guard" approach, nobody gets in without approval.
I'd highly advise installing the free VirtualBox and loading a free ISO of Linux Mint DVD 32 bit 10.10
That is not a realistic suggestion for the average person, who will have neither the desire nor the knowledge to run Linux.
Well note that I placed a condition on that advice, "if one likes surfing the backalleys of the Internet" as all browsers are venerable to some extent from direct website intrusions. So another "compartmentalization" level is required for sites that are prone to that sort of behavior which use images or warz as click bait.
And mind me saying Thomas, it's rather presumptious of you to dictate what another would like or not like.
Remember Apple opened the door to multiple operating systems running on their hardware, the PPC days are long gone, a brave new world is here where one can run all the major operating systems on one machine.
Heck, Steve Jobs even used Linux on his Pixar renderfarm, I bet his MacPro runs everything under the sun just like my 17" Quad does.
Apple is the second largest grossing corporation in the world next to Exxon, professional IT people like myself use Mac's now because of their ability to run all major operating systems. It's looking rather sad showing up to the job dragging a ugly bulky Dell when one can have a slim sexy looking silver MacBook Pro.
So no need to get fan boy defensive any longer.
Note that even folks with Safari's Open "safe" files after downloading option turned off have been affected by opening the installer manually.  And some have been alerted to the presence of malware by the automatic appearance of the installer.  I'd still agree, though, but would add that you should keep your Downloads folder cleaned out, so that any suspicious items that turn up will be easily recognized, and not mistaken for something you downloaded earlier. 
As to Click2Flash, I think nobody should be on the web without it!  I don't trust Flash as far as I could throw Adobe.
 This should have been #1!  AV software has struggled to keep up with all the variants of MacDefender, malware sites move on sometimes an hour-by-hour basis and malicious code sneaks into trusted sites.  In all, no automated defense tool will protect you from a new threat...  only your "wetware" can do that!
Well at least we agree on something, I actually don't approve of anyone using Safari AT ALL, because of it's lack of a NoScript option and failing every Pwn2Own contest.
But there are those who will, by stubborness or brand loyalty, will continue to use Safari so I recommend at least a partial security solution.
And since the MacDefender trojan uses Javascript, not Flash, Click2Flash offers little protection, just another preventative measure against other attacks.