Antivirus software from Sophos Plc, Abingdon, Oxfordshire, England (www.sophos.com) that runs in a wide variety of environments including Windows, Mac, Linux, Unix, NetWare and Network Appliance storage systems. Used worldwide, Sophos is noted for its fast performance.

Scan Once and Create a Checksum
Instead of scanning for all virus signatures each time a file is opened, Sophos performs a full scan on the file one time. If the file is free of viruses, Sophos creates a checksum for the file that it stores in a database. The next time the file is opened, Sophos recomputes the checksum and compares it against the stored checksum. If they match, the file has not been altered. A non-match means the file has been changed, and a full scan is performed against the file.