D. Beecroft Fremont High School 2009-2010 VIRUSES.

D. BeecroftFremont High School

2009-2010

VIRUSES


2009-2010

Computer Virus

A virus is a small piece of software that piggybacks on real programs.

For example, a virus might attach itself to a program such as a spreadsheet program. Each time the spreadsheet program runs, the virus runs, too, and it has the chance to reproduce (by attaching to other programs) or wreak havoc.


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Spreading Viruses

Viruses spread because people distribute infected files by exchanging disks and CDs, sending e-mail attachments, and downloading documents from the Internet.

When you open the infected file, the virus opens and waits to infect the next program you run or disk you use.


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Spreading Viruses (continued)

Viruses have the ability to lurk in a computer for days or months, quietly replicating themselves.

You may not even know your computer has a virus, thus making it easier to spread the virus.


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Trigger Events

Trigger event may be a set of circumstances such as a particular date, a change in some item of data or the absence of a message from their creator.

Time Bomb– Triggered by reaching some preset time, either once or

periodically. Example: Michelangelo virus - 1991

– Damaged files on March 6, the artist’s birthday

Logic Bomb– Programs designed to implement some action, usually malicious or

fraudulent, in response to a trigger.


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Classification of Viruses


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File Virus

File viruses infect executable files by inserting their code into some part of the original file so that the malicious code can be executed when the file is accessed.

Usually infects executable files, which are the main component of a program or application.– Example: Chernobyl – April 16, 1999

– First virus known to have the power to damage computer hardware. The activated viral strain attempts to erase the hard drive and overwrite the system's BIOS as well.


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Boot Sector Virus

Infects hard drives and floppy disks by putting itself on the boot sector of the disk, which has the code that is run at boot up.

Cause widespread damage and recurring problems– Example

Stoned Virus– Discovered in December 1987, the Stoned virus was the

first MBR infector and is thought to have originated in New Zealand.


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Macro Virus

Macro– A miniature program that usually contains

legitimate instructions to automate a document or task

This virus infects a macro– Example: Melissa Virus – March 1999

– An e-mail attachment that, when opened, disables a number of safeguards in Word 97 or Word 2000, and, if the user has the Microsoft Outlook e-mail program, causes the virus to be resent to the first 50 people in each of the user's address books.


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Other Viruses


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Trojan Horse

Appears, to the user, to perform a desirable function but, in fact, facilitates unauthorized access to the user's computer system.

Different from a virus because it does not make copies of itself.

Different tasks that can be affected– Stealing passwords– Deleting files


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Trojan Horse Example


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Worm

Self-replicating computer program. It uses a network to send copies of itself to other nodes (computers on the network) and it may do so without any user intervention.

Example– ILoveYou Virus (e-mail virus) - 2000

The virus overwrote important files, as well as music, multimedia and more, with a copy of itself. It also sent the virus to everyone on a user's contact list.


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Worm Example


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Protecting yourself from viruses

Antivirus software – Software that is used to prevent, detect, and remove

malware, including computer viruses, worms, and trojan horses. Such programs may also prevent and remove adware, spyware, and other forms of malware.

– Examples of Best AntiVirus Software VIPRE BitDefender Kasperski Panda Norton McAfee


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Resource

Fuller, Floyd. Computers: Navigating Change. EMC Paradigm, 2002.

Parsons, June Jamrich, and Dan Oja. Computer Concepts. Boston: Course Technology - Thompson Learning, 2002.

D. Beecroft Fremont High School 2009-2010 VIRUSES.

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