Mac users have enjoyed some anonymity when it comes to concerns over viruses and trojans due to the small market share Mac computers have traditionally had compared to Windows-based PCs. That may be changing though. As our sister site PCMag.com points out, the Windows PC market share is on the verge of falling below 90% this year indicating there are some weak points in the armor of Microsoft’s dominant operating system.The market share held by Macs may only be around 5%, but it has gained some momentum thanks in part to the crossover appeal of iPod, iPhone and iPad owners. Unfortunately, popularity isn’t always a good thing when it comes to security. As Mac computers make themselves increasingly known on the radar, hackers are beginning to take an interest as demonstrated by a new, not yet finished Mac OS X backdoor trojan reported by Sophos.Sophos highlighted the new trojan in its Naked Security blog, stating that after analyzing a sample of the trojan they have determined it to be a variant of the Remote Access Trojan (RAT) for Windows known as darkComet. Sophos calls the trojan OSX/MusMinim-A, or MusMinim for short, though the trojan calls itself BlackHole RAT.A hacker able to take control of a Mac using the trojan will be able to:Place text files on the desktopSend restart, shutdown and sleep commandsRun arbitrary shell commandsPop-up a fake administrator password window to phish the targetSend URLs to the client to open a websitePlace a full screen window with a message that only allows a user to click reboot. The current default message states:I am a Trojan Horse, so i have infected your Mac Computer. I know, most people think Macs can’t be infected, but look, you ARE Infected!I have full controll over your Computer and i can do everything I want, and you can do nothing to prevent it.So, Im a very new Virus, under Development, so there will be much more functions when im finished.Read more at the Naked Security blogBrian’s OpinionBeing a Mac user, I have to admit I think Windows gets a bad rap. While the Windows operating system has indeed been found to have security vulnerabilities at times, those vulnerabilities rise to the surface quicker than any other operating system. After all, if you are a hacker and want to do some serious damage are you going to spend your time and energy on an operating system with less than 90% market share? Of course not, that’s why most trojans and viruses target Windows because there is the potential for more collateral damage.Up until now, I think Mac OS X has benefited greatly from Windows’ popularity, but the tide may be turning. While 5% market share is nothing to crow about, few would argue that Apple has made quite a name for itself due to the popularity of its iPod, iPhone and iPad devices. Consumers who own these devices are typically the ones helping to drive up Mac market share as they extend their Apple experience to a computer. It’s the popularity of these devices and the increasing market share of Macs that may be forcing hackers to take a second look at Mac OS X due to the media coverage a successful virus or trojan on the OS would generate.The simple answer for Mac users now is to begin to take security threats more serious. They can begin by installing a free anti-virus for Mac like the one offered by Sophos. Think of it like insurance: hopefully you won’t need it, but if you do it will be there.