If imitation is the sincerest form of flattery, then this has to be good news for Microsoft. F-Secure recently found a piece of malware that spoofed Microsoft Security Essentials. Here’s a link to the article:
"Not only does this fake took steal Microsoft's brand, it also features a bizarre matrix display of 32 antivirus products, offering to locate you a tool that would be capable of fixing your machine as 'Microsoft Security Essentials' can't clean the malware it found," F-Secure said. "In reality, this is all fake, and the tool has not found an infection in the fail it claims."
Microsoft only released their free A/V product a little over a year ago which is not a lot of time to gain market share amongst its competitors. The fact that malware authors have taken the time to notice it and then start spoofing it suggests it has made an impact on the general consumer base and underground economy. They wouldn’t spoof it if nobody recognized it, which means that there has to be at least some degree of ubiquity.
Of course, the flip side is that is is unfortunate that there are even vulnerabilities for malware authors to exploit and that they can use this to push their evil merchandise. It’s kind of like making the playoffs but losing your starting quarterback in the last game of the season.