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Unit 11: System Security

These security attacks make the study of security measures very essential for the following Notes
reasons:
1. To prevent loss of data: You don’t want someone hacking into your system and destroying
the work done by you or your team members. Even if you have good back-ups, you still
have to identify that the data has been damaged (which can occur at a critical moment
when a developer has an immediate need for the damaged data), and then restore the data
as best you can from your backup systems.
2. To prevent corruption of data: Sometimes, the data may not completely be lost, but just be
partially corrupted. This can be harder to discover, because unlike complete destruction,
there is still data. If the data seems reasonable, you could go a long time before catching
the problem, and cascade failure could result in serious problems spreading far and wide
through your systems before discovery.
3. To prevent compromise of data: Sometimes it can be just as bad (or even worse) to have
data revealed than to have data destroyed. Imagine the consequences of important trade
secrets, corporate plans, financial data, etc. falling in the hands of your competitors.

4. To prevent theft of data: Some kinds of data are subject to theft. An obvious example is the
list of credit card numbers belonging to your customers. Just about anything associated
with money can be stolen.
5. To prevent sabotage: A disgruntled employee, a dishonest competitor, or even a stranger
could use any combination of the above activities to maliciously harm your business.
Because of the thought and intent, this is the most dangerous kind of attack, the kind that
has the potential for the greatest harm to your business.

11.3 Program Threats

Any person, act, or object that poses a danger to computer security is called a threat. Any kind
of policy, procedure, or action that recognizes, minimizes, or eliminates a threat or risk is called

a countermeasure. Any kind of analysis that ties-in specific threats to specific assets with an
eye toward determining the costs and/or benefits of protecting that asset is called risk, or risk

assessment. Risk is always a calculated assumption made based on past occurrences.
Threat, on the other hand, is constant. Any kind of asset that is not working optimally and is
mission-critical or essential to the organization, such as data that are not backed-up, is called a
vulnerability, while anything imperfect is called a weakness. Any kind of counter measure that
becomes fairly automated and meets the expectations of upper management is called a control,
and there are many types of controls in a computer security environment, as well as threats, some
of which are given below:
Malicious Threats
Category Threat OSI Definition Typical Be- Vulnerabilities Prevention Detection Countermea-

Layer haviors sures

Mali- Virus Applica- Malicious Replicates All computers Limit con- Changes in file Contain,
cious tion software that within com- Common cat- nectivity. sizes or date/ identify and
Software attaches itself to puter system, egories Limit down- time stamps recover
other software. potentially at- Boot sector loads Computer is Antivirus scan-
For example, a taching itself to Terminate Use only slow starting ners- look for
patched soft- every software authorized or slow run- known viruses
and Stay
ware applica- application Resident media for ning Antivirus moni-
tion in which Behavior cat- (TSR) loading data Unexpected tors- look for
the patch’s egories Application and software or frequent virus related
algorithm is Innocuous software Enforce system failures application
designed to mandatory behaviors
Humorous Stealth (or Change of
implement the Data alter- access con- system date/ Attempt to
same patch on ing Chameleon) trols. Viruses time determine
other applica- Mutation generally Low computer source of infec-
tions, thereby Cata- engine cannot run memory or tion and issue
replicating. strophic Network unless host increased alert
Mainframe application
bad blocks on
is running disks
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