Salami attack

In the salami technique, cyber criminals steal money or resources a bit at a time. The key here is to make the alteration so insignificant that in a single case it would go completely unnoticed. E.g. a bank employee inserts a program, into the bank's servers, that deducts a small amount of money (say Rs. 5 a month) from the account of every customer. No account holder will probably notice this unauthorized debit, but the cyber criminal will make a sizable amount of money every month.

The classic story about a salami attack is the old " collect-the-roundoff " trick. In this scam, a programmer modifies arithmetic routines, such as interest computations. Typically, the calculations are carried out to several decimal places beyond the customary two or three kept for financial records. For example, when currency is in dollars, the round off goes up to the nearest penny about half the time and down the rest of the time. If a programmer arranges to collect these fractions of pennies in a separate account, a sizable fund can grow with no warning to the financial institution.

To quote an example, an employee of a bank in USA was dismissed from his job. Disgruntled at having been supposedly mistreated by his employers the man first introduced a logic bomb into the bank's systems.

Logic bombs are programmers, which are activated on the occurrence of a particular predefined event. The logic bomb was programmed to take ten cents from all the accounts in the bank and put them into the account of the person whose name was alphabetically the last in the bank's rosters. Then he went and opened an account in the name of Ziegler. The amount being withdrawn from each of the accounts in the bank was so insignificant that neither any of the account holders nor the bank officials noticed the fault.

It was brought to their notice when a person by the name of Zygler opened his account in that bank. He was surprised to find a sizable amount of money being transferred into his account every Saturday.

you can know by:

1. your computer shuts down by itself
2. Sites keep opening realy fast by it self
3. you keep getting annoying messages
4. your computer gets really slow
5. if you have a anti virus dececter it might find one
6. YOU SHOULD KEEP AN ANTIVIRUS DECTETOR e.x NOTRON .
7. Your computer keeps restarting it self
8. If you open a website it closes by itself

Resident Virus

This type of virus is a permanent as it dwells in the RAM. From there it can overcome and interrupt all the operations executed by the system. It can corrupt files and programs that are opened, closed, copied, renamed etc.

Examples: Randex, CMJ, Meve, and MrKlunky.

Direct Action Viruses

The main purpose of this virus is to replicate and take action when it is executed. When a specific condition is met, the virus will go into action and infect files in the directory or folder that it is in as well as directories that are specified in the AUTOEXEC.BAT file path. This batch file is always located in the root directory of the hard disk and carries out certain operations when the computer is booted.

Examples: Vienna virus.

Overwrite Viruses

Virus of this kind is characterized by the fact that it deletes the information contained in the files that it infects, rendering them partially or totally useless once they have been infected. The only way to clean a file infected by an overwrite virus is to delete the file completely, thus losing the original content.

Examples: Way, Trj.Reboot, Trivial.88.D.

Boot Sector Virus

This type of virus affects the boot sector of a floppy or hard disk. This is a crucial part of a disk, in which information of the disk itself is stored along with a program that makes it possible to boot (start) the computer from the disk. The best way of avoiding boot sector viruses is to ensure that floppy disks are write-protected and never starting your computer with an unknown floppy disk in the disk drive.

Examples: Polyboot.B, AntiEXE.

Macro Virus

Macro viruses infect files that are created using certain applications or programs that contain macros. These mini-programs make it possible to automate series of operations so that they are performed as a single action, thereby saving the user from having to carry them out one by one.

Examples: Relax, Melissa.A, Bablas, O97M/Y2K.

Directory Virus

Directory viruses change the path that indicate the location of a file. When you execute a program file with an extension .EXE or .COM that has been infected by a virus, you are unknowingly running the virus program, while the original file and program is previously moved by the virus. Once infected it becomes impossible to locate the original files.

Examples: Dir-2 virus.

Polymorphic Virus

Polymorphic viruses encrypt or encode themselves in a different way (using different algorithms and encryption keys) every time they infect a system. This makes it impossible for anti-viruses to find them using string or signature searches (because they are different in each encryption). The virus then goes on creating a large number of copies.

Examples: Elkern, Marburg, Satan Bug and Tuareg.

File Infector Virus

This type of virus infects programs or executable files (files with .EXE or .COM extension). When one of these programs is run, directly or indirectly, the virus is activated, producing the damaging effects it is programmed to carry out. The majority of existing viruses belong to this category, and can be classified depending on the actions that they carry out.

Examples: Cleevix and Cascade.

Companion Viruses

Companion viruses can be considered as a type of file infector viruses like resident or direct action types. They are known as companion viruses because once they get into the system they 'accompany' the other files that already exist. In other words, in order to carry out their infection routines, companion viruses can wait in memory until a program is run (resident virus) or act immediately by making copies of themselves (direct action virus).

Some examples include: Stator, Asimov.1539 and Terrax.1069

FAT Virus

The file allocation table or FAT is the part of a disk used to store all the information about the location of files, available space, unusable space etc. FAT virus attacks the FAT section and may damage crucial information. It can be especially dangerous as it prevents access to certain sections of the disk where important files are stored. Damage caused can result in information losses from individual files or even entire directories.

Examples:

Multipartite Virus

These viruses spread in multiple ways possible. It may vary in its action depending upon the operating system installed and the presence of certain files.

Examples: Invader, Flip and Tequila

Web Scripting Virus

Many web pages include complex code in order to create an interesting and interactive content. This code is often exploited to bring about certain undesirable actions.

Worms

A worm is a program very similar to a virus; it has the ability to self-replicate and can lead to negative effects on your system. But they can be detected and eliminated by anti-viruses.

Examples of worms include: PSWBugbear.B, Lovgate.F, Trile.C, Sobig.D, Mapson.

Trojans or Trojan Horses

Another unsavory breed of malicious code are Trojans or Trojan horses, which unlike viruses do not reproduce by infecting other files, nor do they self-replicate like worms. In fact, it is program which disguises itself as a useful program or application.

Logic Bombs

They are not considered viruses because they do not replicate. They are not even programs in their own right but rather camouflaged segments of other programs. They are only executed when a certain predefined condition is met. Their objective is to destroy data on the computer once certain conditions have been met. Logic bombs go undetected until launched and the results can be destructive.

Besides, there are many other computer viruses that have a potential to infect your digital data. Hence, it is a must that you protect your data by installing a genuine quality anti-virus software.

Improved Answer: OR if you are sexually active you will pass on the disease. -LH