A spyware is a piece of malicious code or program installed in system to monitor activities of a person. A spyware is capable of logging key strokes, it can take screen shots and if there is active Internet connection then it can even mail logs to specified email-address or transfer logs to ftp server.
Beyond just monitoring it can record your computing habits including which site you browse more, at what time you prefer to be on system or amount of time you spend on computer.
A spyware can be used to track all information about your social-networking habits and IRC(Internet Relay Chat) Clients including all major and minor chat clients example: Google Talk, Rediff Messenger, Yahoo Messenger, Microsoft Live Chat, absolutely every thing related to IRC client is exposed to spyware. On the basis of its commercial use and monitoring capabilities spywares are classified as follows,
On Basis Of Commercial Use: Domestic Spywares and Commercial Spywares
On Basis Of Monitoring: Key Loggers, E-mail Loggers/Chat Recorders, Screen Recorders.
Domestic Spywares: This kind of spywares are purchased and used by common people to monitor their system. Most of the times parents install this type of spyware to monitor their children or network admin or a company to monitor computing activities of their employees. The most widely and most powerful use of these spywares are done for hacking purposes only.
Example:
SniperSpy,
Winspy,
Sentry PC,
Spy Agent
Commercial Spywares: Commercial Spywares incude the services included in your Operating System and softwares to monitor event logs and crash reports. The information about software crash is anonymously sent to software vendors, also the reports about user experience, crash, memory dump etc are sent to Operating System Vendor. The only fact is that this type of spying is legal to improve product and provide better and secure service.
Example:Windows and Linux Crash Logs, Virus info in Anti-Virus program, Event Collectors etc.
Key Loggers: Key loggers are spywares specially made to record keystrokes from keyboard. Key Logging can retrieve information about bank account password, online transactions, login passwords etc.
E-mail Loggers/Chat Recorders:These spywares are used to track e-mails and chat report from your IRC. If you use e-mail client like Windows Mail or Mozilla Thunderbird etc. Then these spywares are capable of modifying internal settings to forward mails to attacker's inbox without keeping a track in your Outbox.
Screen Recorders: Screen recorders are capable of capturing screen and send recording using minimum bandwidth. Such monitoring is done by parents on their children to protect them from online pornography.
Example:
Spy Agent,
Winspy,
Sniper Spy
Ok being honest I want to clear that today actually nobody bothers about classification of spyware and reason is quite obvious that spyware manufactures pack their spywares with nearly 90% of features of all types of spywares. So if you don't want to remember classification of spyware then its ok, no problem at all but you must know what is spyware. Sorry forgot you already know that.
