Adware is a summary designation for a type of software created with the intent to conceal advertising within other software. Adware is installed without the user’s knowledge and it often masquerades as a needed complement to other software (such as codec). Adware is one of the lower security risks - its harmfulness lies in the fact that it interupts the work of a user through advertising. It therefore counts as malicious software.
The term adware combines the words advertising supported software or simply ad and software.
How works Adware in practice?
Adware may have different levels of aggressiveness - ranging from banners to pop-ups or the redirection to other pages. Its harmfulness lies mainly in its annoyance of users. Protection from adware is offered by security software (preferably in combination with Antispyware, Antiviruses, Firewalls). Caution is required when installing new software; making sure that it comes only from trusted sources.