Today there are many viruses for Mac OS X, its number is growing every day. Despite the fact that most of viruses, trojans and other malware are created for Windows based operating systems, other operating systems, for example Mac OS X, are also required to be protected by antivirus software.
Thus, when you buy Mac OS, pay careful attention to its protection. Even Apple recommends to use antivirus software to secure the protection of your operating system onits site:
"Security Advice. The Mac is designed with built-in technologies that provide protection against malicious software and security threats right out of the box. However, since no system can be 100 percent immune from every threat, antivirus software may offer additional protection."