An article in Information Security Technical Report [“MaliciousSoftware—Past, Present and Future†(2004, Vol. 9, pp. 6–18)]provided the following data on the top 10 malicious softwareinstances for 2002. The clear leader in the number of registeredincidences for the year 2002 was the Internet worm “Klez,†and itis still one of the most widespread threats. This virus was firstdetected on 26 October 2001, and it has held the top spot amongmalicious software for the longest period in the history ofvirology.
The 10 most widespread malicious programs for 2002
| Place | Name | % Instances |
| 1 | I-Worm.Klez | 61.22% |
| 2 | I-Worm.Lentin | 20.52% |
| 3 | I-Worm.Tanatos | 2.09% |
| 4 | I-Worm.BadtransII | 1.31% |
| 5 | Macro.Word97.Thus | 1.19% |
| 6 | I-Worm.Hybris | 0.60% |
| 7 | I-Worm.Bridex | 0.32% |
| 8 | I-Worm.Magistr | 0.30% |
| 9 | Win95.CIH | 0.27% |
| 10 | I-Worm.Sircam | 0.24% |
(Source: Kaspersky Labs).
Suppose that 20 malicious software instances are reported.Assume that the malicious sources can be assumed to be independent.(a) What is the probability that at least one instance is “Klez?â€(b) What is the probability that three or more instances are“Klez?†(c) What are the mean and standard deviation of the numberof “Klez†instances among the 20 reported?
