The process of securely erasing a hard drive is called formatting.
Formatting is where you delete all the files in your drive and making sure that it is secure. When you format your drive, it erases all the data even viruses stored in your drive. So most of the time, when an IT person thinks that his computer has virus, one option that he can do is do the formatting to make sure that his computer is clean when he reuse it again the next time.