They are choosing to do security updates to their products. The article notes that since the virus was added to the list of malware removed by Microsoft's Mali

They are choosing to do security updates to their products. The article notes that since the virus was added to the list of malware removed by Microsoft's Malicious Software Removal Tool, the numbers of computers infected by it have shrunk significantly. This suggests that the computers will are still infected are those which are not choosing to apply security updates. Regardless of whether Microsoft would be "within its rights" to start something like this, it would still be liable for any damage caused to computers which became broken by the cleaning (see the next to last paragraph of the article).