Microsoft researchers recently discovered a piece of Mac OS X malware that exploits a three-year-old flaw in old versions of Office for Mac. The threat uses a multi-stage attack, just like a Windows virus would. While Microsoft did fix the problem in 2009, the software giant notes that not every machine is up-to-date. The company’s data indicates, however, that the malware is not widespread. “No operating system that exists outside a laboratory is entirely immune to malware,” Microsoft stated on its blog. “As different operating systems continue to gain in popularity they attract more attention from would-be attackers – especially since, as we see in the example analysis above, the techniques and understanding needed to do so may be much the same as those used against other platforms. And even though an operating system may include many risk-reducing mitigation technologies, any machine’s defenses against vulnerabilities are directly related to how current its security updates for applications are kept.” Microsoft concludes by warning users of Office 2004 for Mac, Office 2008 for Mac or Open XML File Format Converter for Mac to update their software in order to protect themselves from possible threats.