A hacker can have different meanings
Hacker (computing), a contentious term used for several types of person:
Hacker (computer security) or cracker, who accesses a computer system by circumventing its security system
Hacker (programmer subculture), who shares an anti-authoritarian approach to software development now associated with the free software movement
Hacker (hobbyist), who makes innovative customizations or combinations of retail electronic and computer equipment
Hackers prospective in the web domain
Hackers target the web application because it easily provides access to the most valuable business assets, such as employee and customer data (like health records and credit card information) as well as corporate proprietary information. While most web sites are heavily secured at the network level with firewalls and encryption tools, these sites still allow hackers complete access to the enterprise through web application manipulation.
Hackers were visionaries who could see new ways to use computers, creating programs that no one else could conceive. They were the pioneers of the computer industry, building everything from small applications to operating systems. In this sense, people like Bill Gates, Steve Jobs and Steve Wozniak were all hackers -- they saw the potential of what computers could do and created ways to achieve that potential.
A unifying trait among these hackers was a strong sense of curiosity, sometimes bordering on obsession. These hackers prided themselves on not only their ability to create new programs, but also to learn how other programs and systems worked. When a program had a bug -- a section of bad code that prevented the program from working properly -- hackers would often create and distribute small sections of code called patches to fix the problem. Some managed to land a job that leveraged their skills, getting paid for what they'd happily do for free.
As computers evolved, computer engineers began to network individual machines together into a system. Soon, the term hacker had a new meaning -- a person using computers to explore a network to which he or she didn't belong. Usually hackers didn't have any malicious intent. They just wanted to know how computer networks worked and saw any barrier between them and that knowledge as a challenge.
more on this here: http://computer.howstuffworks.com/hacker1.htm
Individuals with unethical behaviors are
finding a variety of ways of conducting activities that cause businesses and consumers much grief and vast amounts annually in damages.
The major attack techniques of hackers are:
1.Buffer overflows: overwriting a crafted buffer over the return address of a function.
this can be: Overflowing A Stack Buffer
4.Format String Attacks which belong to the third generation techniques.
more on hackers techniques here: