Spyware has been coined from the base word of spying.
Spyware is a typical type of malware that would spy on the activities of the user without their knowledge. The spread of Spyware is normally through USB drives, email attachments, or through the network.
Unlike viruses, which infect other files and are noticeable through these activities, Spyware normally stays hidden from the users as they are not actively interfering with the functions of a computer.
They passively collect details like bank account details, email addresses, credit card details, etc., and relay them to their original creator. Spyware is also known to collect information regarding the browsing habits of the users and the sites that have been visited by the users.
Based on this data Spyware would present targeted ads to the user through infected browsers thus becoming annoying at times. Spyware is also known to assist in the installation of other malware onto the infected system.
This is mainly done by spyware writers to target infected systems for processing power to perform more complicated attacks on websites and servers of reputed companies. These attacks might include Distributed Denial of Service (DDOS) attacks, major spam outbreaks, etc.
Spyware is also known to hamper the processing of the system which results in a decrease in browsing speeds, changes to browser settings, loss of connectivity or functionality of some important system functions, etc.
Spyware can be removed through free or commercial antispyware tools available in the market.