Viruses and Trojans
What is a Virus?
A computer virus is a program – a piece of executable code – that has
the unique ability to replicate. Like biological viruses, computer viruses can
spread quickly and are often difficult to eradicate. They can attach themselves
to just about any type of file and are spread as files that are copied and sent
from individual to individual.
In addition to replication, some computer viruses share another commonality:
a damage routine that delivers the virus payload. While payloads may only
display messages or images, they can also destroy files, reformat your hard
drive, or cause other damage. If the virus does not contain a damage routine, it
can cause trouble by consuming storage space and memory, and degrading the
overall performance of your computer.
Several years ago most viruses spread primarily via floppy disk, but the
Internet has introduced new virus distribution mechanisms. With email now used
as an essential business communication tool, viruses are spreading faster than
ever. Viruses attached to email messages can infect an entire enterprise in a
matter of minutes, costing companies millions of dollars annually in lost
productivity and clean-up expenses.
Viruses won't go away anytime soon: More than 60,000 have been identified,
and 400 new ones are created every month, according to the International
Computer Security Association (ICSA). With numbers like this, it's safe to say
that most organizations will regularly encounter virus outbreaks. No one who
uses computers is immune to viruses.
What is a Trojan?
A Trojan is malware that performs unexpected or unauthorized, often
malicious, actions. The main difference between a Trojan and a virus is the
inability to replicate. Trojans cause damage, unexpected system behavior, and
compromise the security of systems, but do not replicate. If it replicates, then
it should be classified as a virus.
A Trojan, coined from Greek mythology's Trojan horse, typically comes in good
packaging but has some hidden malicious intent within its code. When a Trojan is
executed users will likely experience unwanted system problems in operation,
and sometimes loss of valuable data.
Trend Micro World Virus Tracking Center
Life Cycle of a Virus
The life cycle of a virus begins when it is created and ends when it is
completely eradicated. The following outline describes each stage:
Creation
Until recently, creating a virus required knowledge of a computer
programming language. Today anyone with basic programming knowledge can create a
virus. Typically, individuals who wish to cause widespread, random damage to
computers create viruses.
Replication
Viruses typically replicate for a long period of time before they
activate, allowing plenty of time to spread.
Activation
Viruses with damage routines will activate when certain conditions are
met, for example, on a certain date or when the infected user performs a
particular action. Viruses without damage routines do not activate, instead
causing damage by stealing storage space.
Discovery
This phase does not always follow activation, but typically does. When a
virus is detected and isolated, it is sent to the ICSA in Washington, D.C., to
be documented and distributed to antivirus software developers. Discovery
normally takes place at least one year before the virus might have become a
threat to the computing community.
Assimilation
At this point, antivirus software developers modify their software so
that it can detect the new virus. This can take anywhere from one day to six
months, depending on the developer and the virus type.
Eradication
If enough users install up-to-date virus protection software, any virus can
be wiped out. So far no viruses have disappeared completely, but some have long
ceased to be a major threat.
Top 10 Tips to Keep Your Computer Virus-Free
1. Install reliable anti-virus software. Anti-virus software scans
files regularly for unusual changes in file size, programs that match the
software's database of known viruses, suspicious email attachments, and other
warning signs. It's the most important step you can take towards keeping your
computer clean of viruses.
2. Don't automatically open attachments. Be sure your email program
doesn't automatically download attachments. This will ensure that you can
examine and scan attachments before they run. Refer to your email program's
safety options or preferences menu for instructions.
3. Scan all incoming email attachments. Be sure to run each attachment
you plan to open through the anti-virus check. Do this even if you recognize and
trust the sender; malicious code, like Trojan horses, can slip into your system
by appearing to be from a friendly source.
4. Get immediate protection. Configure your anti-virus software to
boot automatically on start-up and run at all times. This will provide you
back-up protection in case you forget to scan an attachment, or decide not to.
And in case you forget to boot up your anti-virus software, configuring it to
start by itself will ensure you get immediate protection anyway.
5. Update your anti-virus software frequently. An anti-virus program
is only as good as the frequency with which it is updated. New viruses, worms,
and Trojan horses are born daily, and variations of them can slip by software
that is not current.
6. Don't download programs from the Web. Unreliable sources such as
Internet newsgroups or Web sites that you haven't heard of may be willing
providers of viruses for your computer. Avoid downloading files you can't be
sure are safe. This includes freeware, screensavers, games, and any other
executable program - any files with an ".exe" or ".com"
extension, such as "coolgame.exe." Check to see if the site has
anti-virus software running on their side. If you do have to download from the
Internet, be sure to scan each program before running it. Save all downloads to
one folder, then run virus checks on everything in the folder before using it.
7. Don't boot from a floppy disk. Floppies are one of the most common
ways viruses are transmitted. If you are using a floppy while working on your
computer, remove it when you shut the machine off or the computer will
automatically try to boot from the floppy, perhaps launching any viruses on the
disk.
8. Don't share floppies. Even a well-meaning friend may unknowingly
pass along a virus, Trojan horse, or worm. Label your floppies clearly so you
know they're yours and don't loan them out. If a friend passes you a foreign
floppy, suggest an alternative method of file sharing.
9. Scan floppies before using them. This is always important, but
especially if you are using the disk to carry information between one computer
and another. You could easily pick up a virus from an insecure network and
introduce it into your system. Running a virus scan before launching any of the
programs on the disk will prevent infection.
10. Use common sense. It's always better to err on the side of safety.
If you're unsure about an attachment, delete it. Especially if it's from a
source you don't recognize. If there are tempting animations on a site that look
highly unprofessional, don't download them.
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