COS 116 The Computational UniverseLaboratory 9: Virus and Worm Propagation in NetworksYou learned in lecture about computer viruses and worms. In this lab you will study viruspropagation at the quantitative level. We can also study, to a certain extent, the spread ofhuman disease since it has similar properties as computer viruses. You will first use asimple simulator application to gather data and then use Microsoft Excel to visualize it.The application can model a network of interconnected computers similar to the Internetbut with fewer (up to 100,000) computers. When you set all relevant parameters andclick “Run Simulation,” it simulates the spread of a virus/worm in the network andoutputs some numbers for you to analyze.Hand in your lab report at the beginning of lecture on Tuesday, April 22.Turn in only the Excel charts that are followed by a star (*). Do not turn in the chartswithout a star; they are just for you to visualize the simulation. Make sure each chartis labeled with the Experiment number and Question number, as well as anyrelevant additional information (e.g. particular options). You will not receive creditfor charts that are unlabeled. Also, turn in answers to all questions posed in thebody of the lab and in the “Additional Questions” section.Introduction: Using the Simulator1. Download this file to your Desktop: http://www.cs.princeton.edu/courses/archive/spring08/cos116/lab9_files/vsim.exe2. Double-click the file to run the simulator. Ignore any security warnings. Thesimulator has a variety of options to adjust. These options are explained below.Note that the simulator uses randomnes, especially when using the social networksettings, so your results may not look exactly like your neighbor’s.Figure 1: Simulator interfaceHere is a brief explanation of all adjustable parameters.• Network size: The number of nodes in the network. This can be interpreted as thenumber of computers in a computer network or the number of people in a socialnetwork.• Network type: In a fully-connected network, every node is directly connected toevery other node. In a social network the connections are generated according to arandomized scheme so that the resultant network resembles actual social networksthat have been studied. Though the details of the social network are interesting (feelfree to ask your TA questions) they are not relevant for this lab. You just need toknow that each node is directly connected to at least the number specified in“Minimum Friends” though some nodes may be connected to much more than thisminimum. (In social networks, these are the popular people.)• Initially vulnerable: The percentage of computers that is initially vulnerable toinfection. This models the possibility that some computers may already be patchedagainst a weakness, or that some people are immune to a disease.• Initially infected population: The number of computers that are initially infected.• Time to install: The amount of time before an infected computer begins to spread thevirus to other computers.• Time to spread: The amount of time between infection attempts by an infectedcomputer that is spreading the virus.• Time to repair: The amount of time from infection until the virus is removed and thecomputer is immunized.How infection works:An infected computer spreads the virus by randomly choosing a computer to which it isdirectly connected, every "Time to Spread" seconds. If that computer is vulnerable, thenit will begin spreading the virus "Time to Install" seconds later. However, the good guysmay rush software patches to remove the virus/worm. The "Time to Repair" is the timeafter which the computer is considered repaired -- no longer spreading the virus/worm,nor susceptible to infection again.Interpreting the results using Excel:The simulator outputs periodic counts of vulnerable, infected, and repairedcomputers. You can save this output to a file of type CSV (“Comma Separated Values”),which is a standard format for data files. To graph the data from a CSV file in Excel:1. Double-click the CSV file to open it in Excel.2. Use the mouse to select all the columns and rows that have data (or, to do thiswith the keyboard, press Ctrl + A).3. From the Insert menu, click the Scatter chart type “with only markers.”4. Select File … Save As, and save the file as a *.xls file (not as a CSV file).0200040006000800010000120000 200 400 600 800 1000 1200 Vulnerable Infected PatchedFigure 2: Example chartPart 1: Worms vs. Email VirusesYou may wish to read the lecture notes to refresh your memory about the differencebetween viruses and worms. (Your TA is happy to answer questions.)1. Run the simulator with the settings depicted in Figure 1 above (which are thedefault settings), except set “Time to Install” to 10 seconds. Plot the result in anExcel chart.2. Now select “Social Network” and set “Minimum Friends” to 20. Also, change“Time to Install” to 150 seconds. Run the simulator, and plot the result in anExcel chart.3. Which of the previous simulations is a better model for the spread of worms,and which is a better model for the spread of email viruses? Explain youranswer in terms of what you know about how worms and email viruses arepropagated.4. Report the total number of computers that were infected during eachsimulation. To do this, look at the last line of output for the simulation, and notethe number of infected and repaired computers. The total number of computersinfected during the simulation is the sum of these two numbers.5. The two totals you report in (4) should be similar to each other (if not, see theTA). Still, worms are considered more damaging than email viruses. Explainwhy, based on the charts of the simulations.Part 2: Vulnerability of the Network1. Change back to the default settings (see Figure 1 above), and plot the resultin an Excel chart*.2. Now change “Initially vulnerable” to 50%, and plot the result in an Excel chart.Explain any difference between the two charts.Part 3: Infection Rate1. Change back to the default settings, except set “Time to Spread” to 2 seconds.Plot the result in an Excel chart*.2. Repeat Step 1 for “Time to Spread” values of 4, 6, 8 and 10 seconds. Plot theresults in separate Excel charts*. Hint: It will probably be faster to generate allthe data first, and then create the Excel charts. When saving the output to CSVfiles, use descriptive names so that you don’t
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