What it all boils down to is marketshare. I deal with malware from all ends of the spectrum, and the entire purpose of modern malware is usually one thing. To make money. Whether that be by using that machine in a botnet, stealing banking or other logon info, or by trying to get someone to pay for fake security software, malware has turned into (within the last decade) a major business. Due to lack of enforcement, these things mainly stem from countries with little oversight (African countries, Russia, tiny islands etc) And are hard to take down. The reason Linux has not been mass targeted is that it normally represents the higher end of the user spectrum, whereas windows is the low hanging fruit. Take international pickpockets or muggers. The offenders will find the most vulnerable target who is unaware of their surroundings and unable to defend themselves. Windows is a 60 year old lady in a foreign market with her passport and wallet around her neck wearing bright pink taking pictures and not paying attention. Linux is more like an aware person who has made themselves a hard target just by knowing what not to do. Mac's seem to be the exception for the moment, and this is where I actually happen to see a huge potential for this to change though. More and more instead of the family tech having to support a family windows box, it is simply easier to just tell a novice to get a mac. Once this reaches a certain apex, that is when malware will target it. Just about any system can be compromised, but back to my original point is it worth it (money?)