How computer viruses work

computer virus - an unwanted program that has entered your system without you knowing about 55

5 it - has two parts, which I'll
call the infector and the
detonator. They have two
very different jobs. One of
the features of a computer 60

10 virus that separates it from
other kinds of computer
program is that it replicates
itself, so that it can spread
(via floppies transported 65

15 from computer to computer, or networks) to other computers.

After the infector has copied the virus elsewhere, 70

20 the detonator performs the
virus's main work. Generally,
that work is either damaging
data on your disks, altering
what you see on your 75

25 computer display, or doing
something else that
interferes with the normal
use of your computer.
Here's an example of a 80

30 simple virus, the Lehigh

virus. The infector portion of i
Lehigh replicates by
attaching a copy of itself to
COMMAND.COM (an 8£

35 important part of DOS), enlarging it by about 1000 bytes.

So let's say you put a
floppy containing 90

40. COMMAND.COM into an
infected PC at your office -
that is, a PC that is running
the Lehigh program. The
infector portion of Lehigh 95

45 looks over DOS's shoulder, monitoring all floppy accesses. The first time you tell the infected PC to access your floppy drive, the Lehigh 100

50 infector notices the copy of C0MMAND.COM on the

floppy and adds a copy of itself to that file.

Then you take the floppy 105
home to your PC and boot
from the floppy. (In this case,
you've got to boot from the
floppy in order for the virus
to take effect, since you may 110
have many copies of
C0MMAND.COM on your
hard and floppy disks, but
DOS only uses the
C0MMAND.COM on the 115

boot drive.)

Now the virus has silently and instantly been installed in your PC's memory. Every time you access a hard disk 120 subdirectory or a floppy disk containing C0MMAND.COM, the virus sees that file and infects it, in the hope that this particular C0MMAND.COM 125 will be used on a boot disk on some computer someday.

Meanwhile, Lehigh keeps a
count of infections. Once it
has infected four copies of 130
C0MMAND.COM, the
detonator is triggered. The
detonator in Lehigh is a
simple one. It erases a vital
part of your hard disk, 135

making the files on that part of the disk no longer accessible. You grumble and set about rebuilding your work, unaware that Lehigh is 140 waiting to infect other unsuspecting computers if you boot from one of those four infected floppies.

Don't worry too much U5

about viruses. You may never see one. There are just a few ways to become infected that you should be aware of. The sources seem 150 to be service people, pirated games, putting floppies in publicly available PCs

without write-protect tabs, commercial software (rarely), and software distributed over computer bulletin board systems (also quite rarely, despite media misinformation).

Many viruses have spread through pirated - illegally copied or broken - games. This is easy to avoid. Pay for your games, fair and square.

If you use a shared PC or a PC that has public access, such as one in a college PC lab or a library, be very careful about putting floppies into that PC's drives without a write-protect tab. Carry a virus-checking program and scan the PC before letting it write data onto floppies.

Despite the low incidence of actual viruses, it can't hurt to run a virus checking program now and then. There are actually two kinds of antivirus programs: virus shields, which detect viruses as they are infecting your PC, and virus scanners, which detect viruses once they've infected you.

Viruses are something to worry about, but not a lot. A little common sense and the occasional virus scan will keep you virus-free. Remember these four points:

■ Viruses can't infect a data
or text file.

■ Before running an antivirus
program, be sure to cold-
boot from a write-
protected floppy.

■ Don't boot from floppies
except reliable DOS disks
or your original production
disks.

■ Stay away from pirated
software.

► Vocabulary

fair and square (I. 113) - honestly

it can't hurt (1. 126) - it's probably a good idea

ask 4 Decide whether the following statements are true (T) or false (F) in relation to

the information in the text. If you feel a statement is false, change it to make it true.

1 LJ Viruses cannot be spread through a computer network, only via floppies

transported from computer to computer.

2 LJ The virus will spread as soon as you put the infected floppy in your PC.

3 D The infector works by interfering in some way with the normal use of

your computer.

4 LJ The detonator in Lehigh works by altering what you see on your screen.

5 LJ Most viruses spread through pirated games.

6 ED You should run an antivirus program every time you use your computer.

7 LJ There are not very many viruses in circulation.

8 LJ Virus shields are more effective than virus scanners.

nsk 5 Indicate the line reference where the following ideas are found in the text.

The Lehigh virus must infect four copies ofC0MMAND.COM before damage is done to data.

Always boot your computer from dependable DOS disks or your original disk.

The infector part of a virus must first copy itself somewhere before the detonator part damages the data on your disks.

•Virus scanners discover viruses after the infection and virus shields discover viruses during the infection process.

ask 6 These are answers to questions about the text. Write the questions.

1 Two, one that infects and one that does the damage.

2 By interfering in some way with the normal use of the computer.

3 After it has infected four copies of C0MMAND.COM.

4 Every time you access a hard disk subdirectory or a floppy disk containing
C0MMAND.COM.

5 Yes, by using your common sense and by occasionally scanning for them.

Using the line reference;^ivei), look back in the text and find the reference for the words in italics.

1 They have two very (line 7)

2 is that it replicates itself (line 12)

3 enlarging it by about (line 36)

4 of itself to that file (line 5 3)

5 and infects it (line 73)

6 This is easy to (line 112)

7 which detect viruses (line 131)

8 once they've infected (line 134)

SO

r

Task 8 Using the line references given, look back in the text and find words or phrases

with a similar meaning to:

1 reproduces (lines 10-15)

2 infect (lines 12 17)

3 changing (lines 20-25)

4 immediately (lines (S5-7O)

5 complain (lines SS 90)

Using the line references given, look back in the text and find words or phrases that ha^e an opposite meaning to:

6 reducing (lines 5 5-40)

7 removed from (lines 65-70)

8 records (lines 80-8 5)

9 ignorant (lines 9 5-100)
10 frequently (lines 100-105)

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