Why Windows get attacked

Ever wondered why there are billions(just exaggerating) of viruses which affect Windows OSes? You often hear the confidence with which other OS users talk about the security of the OSes they use- no virus attack, secure system and the like.
The fact is simple. Hackers love the thrill of breaking into closed source OSes and applications. Of course there is no thrill in breaking (breaking not the right word here but I am short of words) into open source OSes and applications.
My sysadmin tells me Windows can be as secure as linux depending on how on configures it. There was this virus which crashes down Windows OS but could not crash down his due to his configurations.
There is nothing like a virus free OS. If hackers set their minds to build viruses for every OS they can develop billions for all OSes but the thrill comes in when the source is closed.