I was always with the group which argued that the Linux does not have worms and virus since it is not popular. Someone who is bent on paining the maximum number of people can easily do it on Windows OS family since it is the most widely used desktop OS. If tomorrow Linux replaces Windows, I feel, the same fate awaits Linux also.
I feel, it is a clear indication that if economy of volumes justifies, black hat hackers will find a way into your Linux system. All that talk about weak passwords etc is impractical since when you reach masses, a number of them will still have vulnerable passwords. In a way Linux has an advantage over windows since the people are more knowledgeable today than in the past as many of them have learned their lessons the hard way using Windows. Even today, I usually find many a edge device with default password. All I can say is, I see a good market for SELinux and related technologies.