HACK or HACKING
The word “Hack” has a lot of meanings in the field of Computer Science: A clever or quick solution to a computer software problem; A good solution to a problem; or A modification of a program or device to give the user access to features that were otherwise unavailable to them.
“Hacking is an act of usinging computer systems to gain knowledge about the system and How does it work?”
Hacking is about gaining more knowledge through the use of computers.

HACKERS
Technically, a hacker is someone who is crazy about computer software and all things that are related to the technical works of a computer. However, What most of the people understand a hacker to be as a ‘cracker’
In a security context, a Hacker is someone involved in computer security, specializing in the discovery of exploits in systems for prevention or in preventing unauthorized access to systems through skills, tactics and detailed knowledge.

CRACKING :
Cracking is the act of breaking the registration, time limits and various other aspects of the software. It is a specialized field which may take to many months or even years to be the master.

CRACKERS :
Cracker is person who tries to gain unauthorized access to computers. This is normally done through a ‘backdoor’ program installed on the computer. A cracker tries to gain access the unauthorized resources through password cracking software, which tries billions of passwords to find the correct one for accessing a computer.

CRYPTOGRAPHY: Cryptography is an art of creating and using cryptosystems. Cryptosystems are methods of rendering messages such that only a select group of people may read them in the original form. This category contains sites related to cryptography.

WHAT DAMAGE A CRACKER CAN DO?
This depends upon what backdoor programs hiding on your PC. Different programs can do different amounts of damage. However, most allow a hacker to operate another program on your PC. This means if a craacker can’t do something using the backdoor program, he can easily put something else on your computer. Cracker can see everything whatever you are doing, and can access any file on your disk. Cracker can write new files, delete files, edit files, and do practically anything to a file that could be done to a file. A Cracker could install several programs on to your system without your knowledge. Such programs could also be used to steal personal information such as passwords and credit card information

HOW DOES A CRACKER WORK?
There are many ways in which a Cracker can hack. Some are as follows
1) NetBIOS :
NetBIOS cracks are the worst kind, since they don’t require you to have any hidden backdoor program running on your computer. This kind of crack exploits a bug in Windows 9x. NetBIOS is meant to be used on local area networks, so machines on that network can share information. NetBIOS can also be used across the Internet - so a Cracker can access your machine remotely.

2) ICMP ‘PING’ (Internet Control Message Protocol) :
ICMP is one of the main protocols that make the Internet work. It stands for Internet Control Message Protocol. ‘Ping’ is one of the commands that can be sent to a computer using ICMP. Usually a computer responds to this ping, telling the sender that the computer does exist. Pings may seem harmless enough, but a large number of pings can make a Denial-of-Service attack, which overload a computer. Also, crackers can use pings to see if a computer exists and does not have a fire wall. If a computer responds to a ping, then the cracker can then launch a more serious form of attack against a computer.

3)FTP (File Transfer Protocol) :
FTP(File Transfer Protocol) is a standard Internet protocol. You may use it for file downloads from websites. If you have a web page of your own, you may use FTP to upload it from your home computer to the web server. However, FTP can also be used by some crackers… FTP normally requires some form of authentication for access to private files.

4) rpc.statd :
This is a problem specific to Linux and Unix. This is a Infamous Unchecked Buffer Overflow Problem. This is where a fixed amount of memory is set aside for storage of data. If data is received is larger than this buffer, the program should truncate the data or send back an error. The memory that has been allocated to it and the data written into parts of memory shouldn’t be in. This can be cause of the crashes of various different kinds. However, a skilled cracker could write bits of program code into memory that may be executed to perform the cracker’s evil deeds.

5) HTTP(HyperText Transfer Protocol) :
HTTP hacks can only be harmful if you are using Microsoft web server software. There is a bug in this software called an ‘unchecked buffer overflow’. If a user makes a request for a file on the web server with a very long name, part of the request gets written into parts of memory that contain active program code. A malicious user could use this to run any program they want on the server.