Hackers is a slang expression that has come to mean "information system attacker" (though at one time the expression 'hacker' was a complement meaning a good programmer capable of resolving difficult problems). To avoid ambiguity, we will use the term "attacker".
Attackers range in both age and skill from young to old, from inept to very skillful. Many articles have been written attempting to quantify what motivates an attacker. It is important that users of information systems understand that attackers do exist, and are becoming more common all of the time. It is also clear that "Typical Stereotypes" (such as bored teenagers seeking a challenge) need to be questioned. More and more, the reasons for an attack are monetary, or malicious rather than 'curiosity-driven'. Incidents of cyber-crime, cyber-activism, cyber-terrorism and cyber-warfare are real and have all occurred at universities. (Universities are common targets.)
A variety of tools and techniques are used to attack information systems. Some of the more common tools are trojan programs (also called 'back doors'), viruses and other malicious code. Technical 'attacker tool kits' are easily found on the internet and information on how to attack information systems is probably at least as easy to find as information on how to protect them (probably easier). Less technical techniques and methods of attack are very common and often rely heavily on user ignorance or poor data practice. Many of these less technical methods (such as simply guessing a password, or watching while some one types) are probably more effective and more difficult to defend against than more technically sophicsticated attacks.