The first version of OSX was released in 1998 in a server version in 1998. So in 16 years there have been no successful computer viruses on OSX FOR macs. There are approximately 50 known Trojan Horse programs — which are not computer viruses, but are malware—in seven OSX Trojan families for OSX, of which OSX will automatically block installation, download, or running. There have been seven known OSX computer virus candidates, all failures.
This "iworm" from Dr. Web, given their suspect history (see their claimed amazing shrinking Macbotnet of 2012 which no one could find a member in the wild), is I believe, merely more FUD. There are too many red flags in their report including their silence on how to avoid infection. . . which would be criminal if it were legitimate.
Since Apple is having an event on October 21st, most likely for the purpose of releasing new Macs, we've entered FUD Season. . . and Dr. Web Is pushing their Mac AV for business product. . . as they were when they launched it and the Macbotnet claim simultaneously two years ago.
Getting antivirus software for a Mac is like giving a condom to a member of the high school A/V club. Sure, there's an outside theoretical chance it might actually be useful for its stated purpose, but only in cases where at least one person has made a serious lapse in judgement.
The only computer that is invulnerable is one that is on its own power supply, in a secure structure, on no network.
That’s a fact.
But, that said, the Mac OS is pretty secure for the most part.