Book : Probability and Statistics for Computer Scientists Chapter 5 Exercise Pro
ID: 3592155 • Letter: B
Question
Book: Probability and Statistics for Computer Scientists
Chapter 5
Exercise Problem 5.9
(Computer project) Twenty computers are connected to a network. One computer becomes infected with a virus. Every day, this virus spreads from any infected computer to any uninfected computer with probability 0.1. Also, every day, a computer technician takes 5 infected computers at random (or all infected computers, if their number is less than 5) and removes the virus from them. Estimate:
(a) the expected time it takes to remove the virus from the whole network; (b) the probability that each computer gets infected at least once;
(c) the expected number of computers that get infected.
How to approach this problem?
Explanation / Answer
Imagine getting a computer virus attack while you’re working on a tight deadline. Your laptop screen goes black right before your eyes. In a split second, everything you have worked on for the last two weeks is all gone.
A virus attack on a personal computer is a nightmare for anyone, from the CEO with sensitive files in his or her laptop to the independent professionals and freelancers who depend on their computers to make money. There are direct and indirect costs that you will have to bear when a virus strikes your laptop.
Let’s see how they add up.
Virus attack cost no. 1: Hiring an expert can cost a lot of money
For many of us who know nada about the inner workings of a computer, the easiest way to restore things would be to call an expert. But expert help can be costly.
First off, getting a computer technician to check your laptop and find out the problem already costs money. Some repair shops may give you a free assessment, but others charge a minimum of $35 for a diagnostic charge.
Further, once the technician knows what the problem is, the repair is often charged by the hour, with rates usually from $50 to $70. If it takes your repairman six hours to get everything in order, that translates to at least $300—and that’s only the technician’s fees.
Rates are cheaper if you’re able to bring your infected laptop to the computer shop, but getting a technician come over on site can run up your tab by an additional $10 an hour. Some technicians also charge an additional call-out or travel fee, anywhere from $35 to $60, depending on how far away your location is from your computer repair store. Getting remote assistance is even more expensive, with some computer shops charging at least $70 per hour for accessing your laptop remotely and fixing it from there.
Cost: Anywhere from $100 for a quick fix, to more than $300 for total repair.
Tip: Installing a paid antivirus program in your computer may cost you anywhere from $40 a year to a one-time charge of $90, but this expense will surely you save a lot of money that you may need to fix an already infected laptop, as well as spare you the added stress.
Virus attack cost no. 2: You’ll have to pay for new programs
If your technician is able to restore everything without the need for a new operating system or new parts, good for you. In a worst-case scenario, you’ll have to shell out more than $80 for a new operating system; around $139.99 to as much as $399.99 for a Microsoft Office package with Word, Excel, PowerPoint, and OneNote (or free—if you prefer open-source applications); as well a new virus program to protect you against future virus infections.
McAfee’s Total Protection virus program starts at $89.99, and its Advanced Troubleshooting program can cost as much as $129.95, while basic virus protection at Norton costs $39.99 a year for one computer.
Read more: How Going Out To Lunch Can Actually Save You Money
For scenarios 1 and 2, you may need emergency cash to tide you over to the next payday. In case you need a loan now, you can check the tips here for loan options. Your goal is to fix your computer asap; paying for an extra interest may be worth it than waiting for the next payday to get rid of the virus.
Cost: Anywhere from $260 for all basic applications to as much as $560 for top-of-the-line programs.
Tip: Be mindful of the sites you visit and the files you download. Likewise, considering how expensive it can get to purchase and install office applications all over again when your laptop gets infected with a virus, it really does make sense to get an antivirus program to begin with or be a little more alert when downloading programs or files to your computer. If you’re not yet ready to purchase an antivirus full version, you can download a freeware or trial version. The sooner you got your antivirus running the safer for your laptop.