BASED on a very recent report, Microsoft is worst at patching and Stuxnet is an issue we covered in [1, 2, 3, 4, 5, 6, 7]. Many large companies may be affected and lives are at stake. According to this, "Stuxnet attackers used 4 Windows zero-day exploits":
The attackers behind the recent Stuxnet worm attack used four different zero-day security vulnerabilities to burrow into — and spread around — Microsoft’s Windows operating system, according to a startling disclosure from the world’s largest software maker.
Two of the four vulnerabilities are still unpatched.
But improvements in the Windows operating system – and Apple and Linux's long-standing built-in defenses – have some wondering if consumers still need to add an anti-virus program to their computers. The answer differs, depending on who you talk to.
[...]
Linux-based systems, however, tend to have a much higher level of built-in security, as most Web servers run on Linux.