Data is protected from viruses by a scanning service, vscan, that uses various scan engines. A scan engine is a third-party application, residing on an external host, that examines a file for known viruses. A file is a candidate for virus scanning if the file system supports the vscan service, the service has been enabled, and the type of file has not been exempted. The virus scan is then performed on a file during open and close operations if the file has not been scanned with the current virus definitions previously or if the file has been modified since it was last scanned.
The vscan service can be configured to use multiple scan engines. It is recommended that the vscan service use a minimum of two scan engines. The requests for virus scans are distributed among all available scan engines. Figure 9, Table 9, Antivirus Scan Engine Software shows the scan engines that are supported when configured with their most recent patch.