The correct answer is: C. Easier.
Standardization of Microsoft programs and the Windows operating system has made the spread of viruses easier because it has created a larger target audience for viruses. With more people using the same software, it is easier for viruses to spread from one computer to another. Additionally, the standardization of these programs has made it easier for virus writers to create viruses that can infect a wide range of computers.
Option A is incorrect because standardization has made it easier for viruses to spread, not more complicated. Option B is incorrect because standardization has made it easier for viruses to spread, not more difficult. Option D is incorrect because standardization has made it easier for viruses to spread, not slower.