When we want to defend ourselves against computer viruses we must protect system's files (operating systems, drivers and other applications) against modification. When we prevent the system from running unknown and unsafe files  therefore we remove the space where computer viruses and hackers can cause damage.


A computer virus is a malware program that, when executed, replicates by inserting copies of itself (possibly modified) into other computer programs, data files, or the boot sector of the hard drive; when this replication succeeds, the affected areas are then said to be "infected".