Article Source : http://lifehacker.com/spyware/
The vast majority of Mac users do absolutely nothing to prevent malware or viruses from infecting their systems, and very few of them have experienced anything that would make them think twice about it. The fact is, however, that Mac malware does exist, and there are tools available to ensure that your Mac is as safe as possible from emerging threats.
Apple itself is straightforward about the fact that OS X isn't impervious to attack. If you go looking, you can find this bit of instruction:
Run an antivirus program if you find any suspicious files or applications, or if you notice any suspicious behavior on your computer. - Apple Support
The argument that OS X is inherently secure enough to dodge nasty things isn't untrue, it's just incomplete. Snow Leopard does have its own built-in malware detection service, but it's usually months behind the databases provided by security firms like Sophos. OS X is a UNIX system, so it's very strict about file permissions and user accounts, but malware doesn't need an administrator account to steal your personal information.
You don't have to be "cruising the red-light district" of the internet to be at risk, either. Take the MacDefender problem as an example. MacDefender, along with variants MacSecurity and MacProtector, is malware that tricks users by looking like it's actually an anti-malware app, and it usually shows up when a poisoned image or link is clicked in an otherwise innocent list of search results. The same trick is often used for fake utility apps like movie players or download managers.
While it's true that Windows is and always has been the primary target for malware, it really comes down to market share. Apple's rise in popularity over the last few years can only be calledmeteoric, so the days of feeling safe just because nobody makes malware for Macs are numbered.
Does that mean you're likely to get infected with something today? Not likely. Mac users can probably keep doing nothing for a couple of years before change is forced on them, but there's no reason to sit back and wait for it. Whether its spyware, viruses or trojans, there are tools available. So, let's take a look at a few of the best options available today that can help protect your Mac.
Little Snitch ($29.99)
Little Snitch isn't technically an antivirus or anti-malware app. It's a service that runs in the background as an interactive firewall. Any app that tries to communicate with another system, whether it's over the network or on the other side of the planet, has to go through Little Snitch. The first time an app tries to make a connection, Little Snitch pops up a request box, and you can choose to allow the connection or have it blocked. You also choose whether you want that choice to be temporary or permanent, and you can alter the "rules" you make at any time. Little Snitch also has a small status window that shows you exactly what's communicating with the outside world at all times, and it shows you where the data is being sent. You can try Little Snitch for a short period, but it's well worth the $29.99 price point. [Little Snitch]
Sophos Free Antivirus for Mac (Free)
Sophos is one of the most trusted authorities on malware and viruses in the industry, and their free offering for OS X is well worth the download if you're feeling insecure. It's extremely user-friendly and never tries to push you to "upgrade" to a paid version. It comes with its own uninstaller (which is actually rare) and it can scan networked drives (which is even rarer). While you're using your Mac, it constantly scans in the background for viruses and known malware threats, along with any suspicious signs of unknown malware threats. It doesn't put a noticeable dent on your system's performance, and Sophos is extremely quick to react to emerging threats (which means you'll always have up-to-date protection). Best of all, of course, is the fact that it's all free. [Sophos]
ClamXav (Free)
ClamXav (Clam Antivirus for OS X) can look daunting to more inexperienced users, but it's actually pretty simple and very powerful for the tiny footprint it has. It puts nearly no drain on your system while running in the background, and you're able to pre-define what folders or drives are scanned in real-time. Virus/threat definitions are updated on a daily basis, and the user always maintains control because everything ClamXav does can be monitored. Whether you're running a system-wide scan, or just running ClamXav in the background, you can actually sit and watch the log file to see each and every file as its scanned. ClamXav is open source and free. [ClamXav]
MacScan ($29.99)
MacScan isn't a normal antivirus/anti-malware app. Instead of running in the background, MacScan is meant to be run by the user, then closed when finished. It scans the system for all sorts of malware, but it differs from others by specifically targeting cookies. This isn't necessarily a bad thing, but it can get pretty annoying when your anti-malware scanner pops up with 27 alerts because of cookies picked up at major web sites. On the other hand, it can be very useful for users who want to rid their system of every last "tracking" cookie. The problem is that MacScan pushes very hard to get you to upgrade to the full version, and because of that, the free version is all but crippled. If you were to purchase the full version, it would cost you $29.99. [MacScan]
ESET Cybersecurity for Mac ($39.99/year)
ESET, like Sophos, is a major player in the antivirus/anti-malware industry, and their Mac offering is extremely sleek. It's not all looks, either; ESET Cybersecurity is the total package. User control is a big selling point for the app, beginning with the installation options. It's got a surprisingly small footprint, so it doesn't slow down your system while running in the background, and it's extremely user-friendly. ESET's threat database can update daily, or every hour—it's your choice. The sleek interface, ease of use, scanning speed, and control options are all major pluses for the app, but ESET's effectiveness is what really makes it worth a yearly fee. It consistently scores higher than most other antivirus apps in third-party tests. A single year's license will cost you $39.99, but you can try it free (full-featured) for 30 days. [ESET]
Kaspersky Anti-Virus for Mac ($39.99/year)
Kaspersky's offering for Mac is very full-featured and user-friendly, like ESET, but differs in that it has fairly high system drain compared to other apps on the list, and includes link-checking extensions for Chrome, Safari, and Firefox. The main interface looks simple, but it's got very granular controls in its preferences. A year's subscription for Kaspersky Anti-Virus for Mac costs $39.99, but you can try it free for 30 days. [Kaspersky Labs]
Others
iAntiVirus and VirusBarrier Express are both simplistic options for Mac users, but neither does anything special, or better than even a free offering like Sophos. VirusBarrier Express is especially known now for dumping features in an attempt to force users to upgrade to the paid VirusBarrier Plus, which still offers nothing that would place it above alternatives.
When it comes down to it, you should always use a free trial and evaluate whatever choice you make, and see for yourself whether it's a good fit for the way you use your system. Don't feel pressured to use an expensive solution, either. The risk of malware striking Mac users may be higher now than in previous years, but it's still a low risk. If nothing else, you can help Windows-using friends by catching potential threats to them.
The lightweight 
Available in both freeware (Home) and shareware (Professional) flavors, Avast Antivirus is the happy home of many an AVG-switcher. Avast is slightly heavier on system resources, but users argue its excellent protection more than makes up for the increased footprint. The freeware version will cost you an email address to get a free registration code from their website.
According to many of its users, 
Fans of shareware antivirus app 
