An organization file system was attacked by a virus. The word documents under at

Question

An organization file system was attacked by a virus. The word documents under attack has an
      estimated value of $14,250. The loss of data, the theft of information, and threats that might
      cause a delay in processing, estimated a loss of about one-third (1/3) of its volume.

     1. Calculate Estimate potential losses (SLE) - This step involves determining the single loss
         expectancy (SLE).

2. The threat analysis on organizational historical data show from the company’s own experience and auditing its logs survey show that the likelihood of such attacks could happen every 3 months. Calculate the annual rate of occurrence (ARO).

3. Determine the potential loss and rate per year to determine the magnitude of the risk. This is expressed as annual loss expectancy (ALE).

A. Lisa is the new CTO at your organization. She wants to ensure that critical business systems are protected from isolated outages. Which of the following would let her know how often these systems will experience outages? (Explain your answer)

A. MITM

B. MTBF

C. MTTF

D. MTTR

B. Let's say we monitored a website during 24 hours (which translates to 86,400 seconds), and in that timeframe the website went down 5 times for an added time
to all failures of 30 minutes.

a) Calculate MTTR

b) Calculate MTBF

c) Calculate Availability

Explanation / Answer

1. Single Loss Expectancy(SLE) is calculated as:

                  SLE = (asset value) * (exposure factor).

     Here clearly the asset value is $14,250 and the exposure factor is over the asset how much impact the risk puts. So here the exposure factor is 1/3.

                SLE = $14250 * 1/3 = $4750.

2. The attack can happen in every 3 months. There are 12 months in a year. So annual rate of expectancy will be 12/3 = 4.

3. Annual Loss Expectancy(ALE) is calculated as:

                     ALE = (Annual Rate of Expectancy) * (Single Loss Expectancy)

As previously Annual Rate of Expectancy and Single Loss Expectancy both calculated as 4 and $4750 respectively,

               ALE = 4 * $4750 = $19000.

A. The correct answer will be option C:MTTF. Mean Time To Failure(MTTF) indicates the expected time to failure for a system which is non-repairable.

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