As Malware
One form of malicious software is that which presents unwanted advertisements to the user of a computer. These advertisements can be in the form of a pop-up. The term adware is sometimes used to refer to this type of malware. When malware observes and interacts with the computer user's activities without their consent, it is called spyware.
Programs have been developed to detect, quarantine, and remove advertisement-displaying malware, including Ad-Aware, Malwarebytes' Anti-Malware, Spyware Doctor and Spybot - Search & Destroy. In addition, almost all commercial antivirus software currently detect adware and spyware, or offer a separate spyware detection package.
Read more about this topic: Adware