This is a common misconception among Mac users and die hard fans of it. You are right, it is hard to believe that an OS can never be affected by a virus or any other malicious program.
I have a list of things below, about 10 of them, which answer your question and explain about Mac, Windows, Viruses and their relation to each other.
1. The Virus – Viruses are mainly programs that can infect a computer, duplicate itself and spread to other computers. A Virus is not to be mistaken for other types of malware, such as Trojans, spyware, root kits, adware, worms and more. A true virus can spread from one computer to another through the use of CD’s, DVD’s, flash disks, emails, the internet, and more.
Computer Viruses are same as the Human Virus flu, can infect its host and spread to another.
2. Why are there viruses – Short answer: Money. Intruders, programmers and alike make viruses to for business. First they create viruses which of course they have a cure for. Once a virus infects a computer host, the owner will definitely want to fix it. That’s where the business starts. The people who programmed the virus will say and prove they have a cure for it. As the virus spreads and more machines get infected, people and companies including companies who make Anti viruses will buy the cure. Sometimes, although they won’t admit, it’s the Antivirus companies themselves who either make it or employ people who do. It’s a simple Supply and Demand.
3. “How is it possible and what are the reasons of Too much viruses in Windows Operating System?” – It is said that only 4% of the world represent those who use MAC OS X. Therefore the opportunity is far better for Virus makers to spread their malware to Windows Operating Systems than to Macs. By being able to seize thousands and millions of PC’s across the globe, virus makers put their money in the bank.
4. “Is it true or not? I want to know because if it is true i will throw my Windows Operating system in the garbage. ” – No, it isn’t true. So don’t throw your Windows yet. Although Viruses and other malware are a rare occurrence in Macs, it doesn’t mean that there are none.
5. OSX/Leap-A (also known as OSX/Oompa-A) – Is known to be the first ever virus for Mac. This worm, which was detected by Sophos Anti-Virus for Mac Home Edition, spreads itself in the iChat instant messaging. It forwards itself as a file called latestpics.tgz to the buddy list contacts of the infected user. When the latestpics.tgz file is opened, it disguises its contents with a JPEG graphic icon, to fool people into thinking it is harmless.
6. OSX/Inqtana-A – Is another worm for the Mac OSX. This one spreads itself between Macs via a Bluetooth vulnerability known as CAN-2005-1333. This worm appeared within days after the discovery of Leap-A in early 2005. By mid 2005, Apple released a patch preventing the spread of the worm.
7. Mac fake Antivirus – Early this May, Google has been hit with a massive SEO Poisoning targeting both Windows and Mac. When searching for images, under hot topics like Osama Bin Laden’s death, Global warming, Mother’s day, etc, a Java-script based scanner shows up as Window’s Security saying that it has detected a few adware and spyware on your PC.
Strangely, it will do the same even when surfing with a Mac. When you click or close the screen, it will prompt you to download a zip file. If you’re using a Mac, it will be saved into something like “BestMacAntivirus2011.mpkg.zip”.
When the trial software is installed, it will do some scanning and use a lot of scare tactics into making you believe your Mac is infected. Although there isn’t any real risks reported, the only danger is if you buy the fake software.
8. Apple Mac malware: caught on camera.
9. BlackHole RAT (OSX/MusMinim-A, or 'MusMinim') – On February this year a backdoor Trojan was detected yet again by SophosLabs. This Trojan places text files on the desktop, sends a restart, sleep or shutdown command, runs arbitrary shell commands, shows a full screen message that only allows you to click reboot, sends URLs to open a website, pops up a fake "Administrator Password" window and more.
However, it actually says that it is not yet complete. It could just be showing intruders and programmers or even Mac fan boys that a virus is possible in a Mac.
10. “I want to know is it real and how is it possible? Is there any possibility of any new virus that will attack Macintosh operating system?” – As you can see from the above examples, viruses and other malware is possible in Mac. With the growing popularity of Apple iPhones, iPods, iPads and Mac, especially since one of Apple’s platform is it’s sharing ability, it’s only a matter of time when they’ll experience the same headache as Windows have been experiencing for a very long time.