Malware
A specific component of anti-virus and anti-malware software, commonly referred to as an on-access or real-time scanner, hooks deep into the operating system's core or kernel and functions in a manner similar to how certain malware itself would attempt to operate, though with the user's informed permission for protecting the system. Any time the operating system accesses a file, the on-access scanner checks if the file is a 'legitimate' file or not. If the file is identified as malware by the scanner, the access operation will be stopped, the file will be dealt with by the scanner in a pre-defined way (how the anti-virus program was configured during/post installation), and the user will be notified. This may have a considerable performance impact on the operating system, though the degree of impact is dependent on how well the scanner was programmed. The goal is to stop any operations the malware may attempt on the system before they occur, including activities which might exploit bugs or trigger unexpected operating system behavior.
Boot sector
As an example, the malware [[Petya (malware)|NotPetya]] attempts to gain administrative privileges on an operating system, and then would attempt to overwrite the boot sector of a computer. The [[Central Intelligence Agency|CIA]] has also developed malware that attempts to modify the boot sector in order to load additional drivers to be used by other malware.
[[Category:Computer file systems]]
[[Category:BIOS]]
[[Category:Booting]]