Sophos
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.
Computing and comparing a file's checksum is considerably faster than matching the file against the huge volume of virus signatures that only continues to grow. See virus.
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| Sophos Vs. Regular Method |
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| As can be seen in this illustration, it takes a lot more time to match a file against all known virus signatures than it does to recompute a checksum and compare it. The full scan has to be performed once in the beginning in order to determine if the file is free of viruses. |