The spyware is any software (spy software), which is usually bundled as a hidden component of shareware or freeware applications that are downloaded from the Internet. Spyware can also be hosted on web pages. It can then be installed on the computers of the users that visit the pages.
Spyware attempts to obtain information from your computer without your permission, typically for advertising purposes. Once the spyware is installed on your computer, it monitors your Internet activity and then reports the information back to its author. Occasionally, the information gathered might be confidential: passwords, credit card numbers, e-mail addresses, etc.
In addition, when the spyware sends out the data obtained across the Internet, it eats up lots of resources and bandwidth, which implies additional detrimental effects.
Note:
In some cases, removing spy software from your computer might affect the
performance of the applications that installed the spyware component in
question. If you wish, you can exclude spyware from the scan or disable
detection of spyware. However, bear in mind that if you do so, your computer
will not be protected against spy software, and your privacy might be
compromised.