A Numbers Game - Why Mac Malware Is On The Rise

Why are Apple PCs being increasingly targeted by malware while they are still less than 10% of the PC population? There is a formula that comes into play, and when the magic numbers are reached - here comes the malware.
...for years, it was believed that Apple’s low market share would protect it from online evildoers. Why waste time coding a virus for Apple’s tiny sliver of users when a much vaster sea of vulnerable Windows machines was waiting to be infected and hijacked for click fraud, denial of service attacks or credit card theft?