Computer Virus

A computer virus is a computer program that can

copy itself and infect a computer

The First Computer Virus

Elk Cloner is one of the first known microcomputer viruses that spread "in the wild," i.e., outside the computer system or lab in which it was written.

It was written around 1982 by a 15-year-old high school student named Rich Skrenta for Apple II systems.

Types of viruses

Boot virusesProgram virusesMultipartite virusesStealth virusesPolymorphic virusesMacro Viruses

Boot Virus Infect floppy disk boot records or master

boot records in hard disks. They replace the boot record program

copying it elsewhere on the disk or overwriting it.

Boot viruses load into memory if the computer tries to read the disk while it is booting.

Examples: Form, Disk Killer, Michelangelo, and Stone virus

Program viruses infect executable program files, such

as those with extensions like .BIN, .COM, .EXE, .OVL, .DRV (driver) and .SYS (device driver).

These programs are loaded in memory during execution, taking the virus with them.

The virus becomes active in memory, making copies of itself and infecting files on disk.Examples: Sunday, Cascade

Multipartite viruses

A hybrid of Boot and Program viruses They infect program files and when

the infected program is executed, these viruses infect the boot record.

When you boot the computer next time the virus from the boot record loads in memory and then starts infecting other program files on disk.

Examples: Invader, Flip, and Tequila

Stealth viruses These viruses use certain techniques

to avoid detection They may either redirect the disk

head to read another sector instead of the one in which they reside or they may alter the reading of the infected file’s size shown in the directory listing.

Examples: Frodo, Joshi, Whale

Polymorphic viruses

A virus that can encrypt its code in different ways so that it appears differently in each infection.

These viruses are more difficult to detect.

Examples: Involuntary, Stimulate, Cascade, Phoenix, Evil, Proud, Virus 101 Examples: Involuntary, Stimulate, Cascade, Phoenix, Evil, Proud, Virus 101 Examples: Involuntary, Stimulate, Cascade, Phoenix, Evil, Proud, Virus 101 Examples: Involuntary, Stimulate, Cascade, Phoenix, Evil, Proud, Virus 101 Examples: Involuntary, Stimulate, Cascade, Phoenix, Evil, Proud, Virus 101

Examples: Involuntary, Stimulate, Cascade, Phoenix, Evil, Proud, Virus 101

Macro Viruses A macro virus is a new type of

computer virus that infects the macros within a document or template.

When you open a word processing or spreadsheet document, the macro virus is activated and it infects the Normal template (Normal.dot)-a general purpose file that stores default document formatting settings.

Every document you open refers to the Normal template, and hence gets infected with the macro virus.

Since this virus attaches itself to documents, the infection can spread if such documents are opened on other computers.

Examples: DMV, Nuclear, Word Concept.

Other kinds of Threats

Adware

Adware or advertising-supported software is any software package which automatically plays, displays, or downloads advertisements to a computer after the software is installed on it or while the application is being used. Some types of adware are also spyware and can be classified as privacy-invasive software.

Malware Malware, short for malicious software, is

software designed to infiltrate a computer without the owner's informed consent. The expression is a general term used by computer professionals to mean a variety of forms of hostile, intrusive, or annoying software or program code. The term "computer virus" is sometimes used as a catch-all phrase to include all types of malware, including true viruses.

Rootkits

Once a malicious program is installed on a system, it is essential that it stay concealed, to avoid detection and disinfection. The same is true when a human attacker breaks into a computer directly. Techniques known as rootkits allow this concealment, by modifying the host operating system so that the malware is hidden from the user. Rootkits can prevent a malicious process from being visible in the system's list of processes, or keep its files from being read. Originally, a rootkit was a set of tools installed by a human attacker on a Unix system where the attacker had gained administrator (root) access. Today, the term is used more generally for concealment routines in a malicious program.

Backdoors A backdoor is a method of bypassing normal

authentication procedures. Once a system has been compromised one or more backdoors may be installed in order to allow easier access in the future. Backdoors may also be installed prior to malicious software, to allow attackers entry

Crackers typically use backdoors to secure remote access to a computer, while attempting to remain hidden from casual inspection.

Spam Spam is the abuse of electronic messaging

systems (including most broadcast media, digital delivery systems) to send unsolicited bulk messages indiscriminately. While the most widely recognized form of spam is e-mail spam

E-mail spam, known as unsolicited bulk Email (UBE), junk mail, or unsolicited commercial email (UCE), is the practice of sending unwanted e-mail messages, frequently with commercial content, in large quantities to an indiscriminate set of recipients.

Spyware

Spyware is a type of malware that is installed on computers and that collects information about users without their knowledge. The presence of spyware is typically hidden from the user. Typically, spyware is secretly installed on the user's personal computer. Sometimes, however, spywares such as keyloggers are installed by the owner of a shared, corporate, or public computer on purpose in order to secretly monitor other users.

Reference

Wikipedia

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