This program then loads the rest of the operating system into memory. Without a boot sector, a computer cannot run software. A boot sector virus infects computers by modifying the contents of the boot sector program by replacing the legitimate contents with its own infected version. The result is you can't get access to your computer's operating system and data. Parasitic Viruses .
Parasitic viruses attach themselves to programs, also known as executables.
When a user launches a program that has a parasitic virus, the virus is given the same rights as the program that the virus is attached because the operating system understands it to be part of the program. These rights allow the virus to replicate itself into memory. An infamous parasitic virus called Jerusalem deletes every program a user launches.