Measures to reduce security threats
- general controls
Contingency planning
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- It is desirable for an organisation to prepare for a major disaster. This is called a
"contingency plan" and its purpose is to enable the organisation to process data
while computer equipment is being replaced and computer files are being reconstructed.
- Elements in the disaster plan include alternative methods of data collection the use of
alternative computer equipment the use of backup computer files temporary distribution of
information
- With respect to data corruption, data-file and database backup plans are devised,
backup, recovery and emergency procedures exist
For example;
- Grandfather-father-son: typically used with sequential systems.
- Fall back and recovery: periodically the contents of files are copied onto a backup
medium. If files are destroyed, the contents are reconstructed from the backup plus the
transaction log or file.
With respect to possible hardware failure
- Backups of all master files are taken at appropriate intervals (perhaps every Friday
night, perhaps with every update). This may not be a full copy of the file but just those
changes, which have been made since the last backup.
- Copies of transaction files are kept for a given length of time eg 4 weeks.
- Lists of masterfile information may be printed regularly and held in the safe (ie on
hardcopy)
- Different generations of important files are kept in different places - eg first level,
a safe in the computer room, second level, a safe in the main office, third level, a safe
in the building across the road.
NB: this must be well documented so the correct transactions are matched
against the correct master when the recovery runs are under way - and none of this is any
use unless the door to the fireproof safe is actually shut.
- In on-line, real-time processing, actual duplicate copies of the master file may be
necessary, with the duplication being enacted every 5 minutes, and every transaction in
the meantime being logged; major users would even have 2 processors capable of acting -
the second picking up automatically if the first goes down.
Definitions of Backup, fallback, recovery
Backup:
Relating to procedures, equipment or data available in the event of failure or
overloading.
Fall-back:
Backup systems brought into use in an emergency situation, especially the reserve database
and programs that would be switched in quickly, or even automatically, in the event of a
detected fault in a real-time system.
Recovery:
Re-instating backup after an error, or failure has occurred.
[Rev: 24/9/98] 3/9/97 © 1996-98 V/2-Com
(Verhaart), P O Box 8415, Havelock North, New Zealand.