6 A computer virus is a little program (insert itself / computer system / damage software and information).

6. A computer virus is a little program (insert itself / computer system / damage software and information).

В данном случае, необходимо использовать слово that или which, так как речь идёт о программе.

Предложение с вставленным словом: A computer virus is a little program that inserts itself into a computer system and damages software and information.

Ответ: A computer virus is a little program that inserts itself into a computer system and damages software and information.