Relates to the constant monitoring of the file system on workstations and servers. For anti-virus software effectiveness, it is important that a computer virus be found and then blocked before it is activated. Therefore, every time a file is accessed for reading or writing, or whenever a program is launched, the on-access scanner is invoked. The on-access scanner literally scans the file. Although on-access scanning is a quite secure way to check for viruses, it is not well liked by sophisticated users because of its adverse impact on performance.

See Also: Anti-Virus Software; On-Demand Scanner; Server; Virus.