Keyloggers sometimes called as keystroke logger or keylogger or system monitor.
Keyloggers main intension is to spy on your computer. It has the ability to record, store   and send by email or FTP, etc.., to a desired person who installed it on your computer..
There are two types of keyloggers Hardware Keylogger, Software Keylogger

Hardware keylogger: It is a hardware device thatmonitors each keystroke a user types on a specific computer’s keyboard. As a hardware device, a keylogger is a small battery-sized plug that serves as a connector between the user’s keyboard and computer. Because the device resembles an ordinary keyboard plug, it is relatively easy for someone who wants to monitor a user’s behavior to physically hide such a device “in plain sight.” (It also helps that most workstation keyboards plug into the back of the computer.) As the user types, the device collects each keystroke and saves it as text in its own miniature hard drive. At a later point in time, the person who installed the keylogger must return and physically remove the device in order to access the information the device has gathered.





Software Keylogger: As per the name it is a small program that has the ability to spy your computer in an incredible way. It do not

require any physical activity to install it on a target computer (Some may require physical contact to install in a target computer) It has the ability to record your passwords, your total internet activity. As it is a software program it can also send LOGS by email or FTP, etc..,
It can also be downloaded unwittingly as spyware and executed as part of a rootkit or remote administration (RAT) Trojan horse. A keylogger program typically consists of two files that get installed in the same directory: a dynamic link library (DLL) file (which does all the recording) and an executable file (.EXE) that installs the DLL file and triggers it to work. The keylogger program records each keystroke the user types and uploads the information over the Internet periodically to whoever installed the program.
IF you want to really spy some one you need then you need a good software to do the job.
As per the personal experience It is best to use SNIPER-SPY.
As it ha s a great features like
Actual Screenshots
Captures a full-size jpg picture of the active window however often you wish.
Websites Visited
Records all website URLs visited in Internet Explorer and Firefox with page title.
Keystrokes in Most Languages
Every keystroke typed into ANY window is logged, including passwords typed.
PC Location Mapping
Logs the IP at each upload to show you physical locations of the PC on a map.
Full Chat Conversations
Records BOTH sides of chats / IMs in Google Talk, Yahoo IM, Windows Live and more.
Applications Executed
Records every application executed by the user including full path and username.
Application Session Durations NEW!
Shows you how long each application was used including start time and stop time.
Automatic User File Uploads NEW!
Uploads an *actual copy* of every document, picture or desktop file changed.
File / Folder Changes
Each time a file or folder changes, the software records the action and the full path.
And many more futures which will help you in spying on your target…
GET YOUR SNIPER-SPY copy now  CLICK HERE

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