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Computer Virus and Antivirus

A presentation by Sumon chakreborty

Roll no-91/CSE/060024

Reg.no-0028438 of 2002-2003

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Agenda

• Computer Virus Concept

• Analyze three common computer viruses

• Antivirus Technologies

• Conclusion

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Computer Virus Concept

• What is Computer Virus?

• Computer Virus Time Line

• Types of Computer Virus

• How does computer virus works?

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Computer virus concept

What is Computer Virus?

• Definition -- Virus: A self-replicating piece of computer code that can partially or fully attach itself to files or applications, and can

cause your computer to do something you don't want it to do.

• Similarities between biological virus (like " HIV " )

and computer virus: • Need a host for residence.

• Capable of self-replicate

• Cause damage to the host.

• Difference: Computer viruses are created by human.

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Computer virus conceptComputer Virus Time Line

• 1949 - Theories for self-replicating programs was first developed.

• 1981 - Apple Viruses 1, 2, and 3 was some of the first viruses in public.

• 1988 – Jerusalem was detected. Activated every Friday the 13th, the virus affects both .EXE and .COM files and deletes any programs run on that day.

• 1991 - Tequila is the first widespread polymorphic virus found.

• 1999 - The Melissa virus, W97M/Melissa, executed a macro in a document attached to an email. Melissa spread faster than any other previous virus.

• 2000 - The Love Bug, also known as the ILOVEYOU virus, sent itself out via Outlook, much like Melissa.

• 2001 - The Code Red I and II worms attacked computer networks in July and August. They affected over 700,000 computers and caused upwards of 2 billion in damages.

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Computer virus concept

Types of Computer Virus • Boot Sector Virus - Michelangelo

Boot sector viruses infect the boot sectors on floppy disks and hard disks, and can also infect the master boot record on a user's hard drive.

• File Infector Virus - CIH

Operate in memory and usually infect executable files.

• Multi-partite Virus

Multi-partite viruses have characteristics of both boot sector viruses and file infector viruses.

• Macro Virus - Melissa Macro Virus

They infect macro utilities that accompany such applications as Microsoft Word, Excel and outlook.

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Computer virus concept

Types of Computer Virus - Continue• Trojan / Trojan Horse – Back Orifice

A Trojan or Trojan Horse is a program that appears legitimate, but performs some malicious and illicit activity when it is run.

• Worm – Red Code

A worm is a program that spreads over network. Unlike a virus, worm does not attach itself to a host program. It uses up the computer resources, modifies system settings and eventually puts the system down.

Worms are very similar to viruses in that they are computer programs that replicate themselves. The difference is that unlike viruses, worms exist as a separate small piece of code. They do not attach themselves to other files or programs.

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Computer virus conceptVirus Characteristics

• Memory Resident:

Loads in memory where it can easily replicate itself into programs of boot sectors. Most common.

• Non-Resident:

Does not stay in memory after the host program is closed, thus can only infect while the program is open. Not as common.

• Stealth:

The ability to hide from detection and repair in two ways.

- Virus redirects disk reads to avoid detection.

- Disk directory data is altered to hide the additional bytes of the virus.

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Computer Virus Concept

Virus Characteristics

• Encrypting:

Technique of hiding by transformation. Virus code converts itself into cryptic symbols. However, in order to launch (execute) and spread the

virus must decrypt and can then be detected.

• Polymorphic:

Ability to change code segments to look different from one infection to another. This type of virus is a challenge for ant-virus detection methods.

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Computer virus concept

How does computer virus work?

• The Basic Rule: A virus is inactive until the infected program is run or boot record is read. As the virus is activated, it loads into the computers memory where it can spread itself.

• Boot Infectors: If the boot code on the drive is infected, the virus will be loaded into memory on every startup. From memory, the boot virus can travel to every disk that is read and the infection spreads.

• Program Infectors: When an infected application is run, the virus activates and is loaded into memory. While the virus is in memory, any program file subsequently run becomes infected.

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Analyze three common viruses

CIH

• Type: Resident, EXE-files

• Origin: Taiwan

• History: The CIH virus was first located in Taiwan in early June 1998. After that, it has been confirmed to be in the wild worldwide. It has been among the ten most common viruses for several months.

• Infects Windows 95 and 98 EXE files, but it does not work under Windows NT.

• After an infected EXE is executed, the virus will stay in memory and will infect other programs as they are accessed.

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Analyze three common viruses

Macro Virus

• What is Macro virus

• A type of computer virus that is encoded as a macro embedded in a document.

• According to some estimates, 75% of all viruses today are macro viruses.

• Once a macro virus gets onto your machine, it can embed itself in all future documents you create with the application.

• In many cases macro viruses cause no damage to data; but in some cases malicious macros have been written that can damage your work.

• The first macro virus was discovered in the summer of 1995. Since that time, other macro viruses have appeared.

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Analyze three common viruses

Macro Virus

• How does it spread?

• When you share the file with another user, the attached macro or script goes with the file. Most macro viruses are designed to run, or attack, when you first open the file. If the file is opened into its related application, the macro virus is executed and infect other documents.

• The infection process of the macro virus can be triggered by opening a Microsoft Office document or even Office Application itself, like Word, Excel. The virus can attempt to avoid detection by changing or disabling the built-in macro warnings, or by removing menu commands

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Analyze three common viruses

I LOVE YOU VBS/LoveLetter is a VBScript worm. It spreads through e-mail as a chain letter.

This worm sends itself to email addresses in the Microsoft Outlook address book and also spreads to Internet chatrooms.

This worm overwrites files on local and remote drives, including files with the extensions .html, .c,.bat,.mp3 etc.

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Antivirus Technologies

• How to detect virus?

• How to clean virus?

• Best Practices

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Antivirus technology

How to detect virus?

• Some Symptoms

• Program takes longer to load.

• The program size keeps changing.

• The drive light keeps flashing when you are not doing anything.

• User created files have strange names.

• The computer doesn't remember CMOS settings.

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Antivirus technology

How to detect virus?

• Use Antivirus Software to scan the computer memory and disks.

• A memory-resident anti-virus software can be used to continuously monitor the computer for viruses.

• Scan your hard disk with an anti-virus software. You should make sure that an up-to-date virus definition data have been applied.

• Use server-based anti-virus software to protect your network.

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Antivirus Technology How to clean virus?

• All activities on infected machine should be stopped and it should be detached from the network.

• Recover from backup is the most secure and effective way to recover the system and files.

• In some cases, you may recover the boot sector, partition table and even the BIOS data using the emergency recovery disk.

• In case you do not have the latest backup of your files, you may try to remove the virus using anti-virus software.

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Antivirus Technology

How to clean virus?

The steps to reinstall the whole system –

1. Reboot the PC using a clean startup disk.

2. Type in MBR to rewrite the Master Boot Record.

3. Format DOS partitions.

4. Reinstall Windows XP or other os and other applications.

5. Install Antivirus Software and apply the latest virus definition data.

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Antivirus Technology Best Practices

• Regular Backup

Backup your programs and data regularly. Recover from backup is the most secure way to restore the files after a virus attack.

• Install Anti-virus Software

Install an anti-virus software to protect your machine and make sure that an up-to-date virus definition file has been applied.

• Daily Virus Scan

Schedule a daily scan to check for viruses. The schedule scan could be done in non-peak hours, such as during the lunch-break or after office hour.

• Check Downloaded Files And Email Attachments

Do not execute any downloads and attachment unless you are sure what it will do

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Conclusion

• Be careful when use new software and files

• Be alert for virus activities

• Be calm when virus attacks

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Thank You