A system had been infected with a virus. After the virus was removed it returned a few days later even though the system had not been connected to a network or external media. Which of the following should be done to remove the virus more permanently?

A.
Enable last known good configuration.

B.
Disable system restore and clean the PC.

C.
Remove all spyware prior to a virus scan.

D.
Run the virus scanner with heuristics.