For many years anti-virus suites have primarily been found and endorsed on Windows platforms only. While they certainly existed on Linux, Mac OS X and even cell phones, it was rare to see them in action and even rarer to see a virus that threatened people enough to warrant such suites in the first place. The increased popularity of OS X is changing that, and for the first time since its release Apple has recommended that Mac users install anti-virus software.
Rattling off a list of anti-virus suites available on the Mac, Apple has encouraged "widespread" use of the programs, claiming it'll make virus writing a more difficult process. Realistically, though, what we see here is a change in the perception that Apple has about their own software in the world today. Typically, they work hard to avoid saying anything negative about Mac OS X, but admitting that users might need an anti-virus suite to stay safe is admitting that the OS is vulnerable after all - something numerous security researchers have been saying for a while.
This year has seen a number of viruses for Mac OS X find time in the public eye. While still not on the monumental level of viruses found on Windows, even Apple is now admitting that the OS alone is not enough to protect a user.