"Adware" is a combination of the words "advertisement" and "software". Adware often makes its way onto a computer when people download free-of-charge shareware and freeware – the downloaded file will contain the program the user wants, but will also include software that displays adverts. One way in which adware programs work is by altering browser settings so unwanted pop-up ads will suddenly appear while surfing the Internet.

If this type of add-on program is also secretly collecting information about the user's system configuration and surfing habits, then it has crossed the blurred line between adware and spyware. The demand for user data that has been collected without authorisation is growing all the time in the advertising industry. Where business involving online advertising space is concerned, the more information that advertisers have about the consumers they are trying to attract, the greater the potential profit margins.

By combining information obtained via spyware with user data that people enter when they register for a software product, for example, advertisers can build up a more precise consumer profile every single time the user visits a web page. It is therefore advisable to carefully weigh the benefits of downloading any software against the risks. The BSI also recommends casting a critical eye over the licence conditions of commercial software to check whether it really is necessary to give consent for the user and device data to be used as described in order for the application to work properly.

Ad blockers are an important way of safeguarding users on the Internet, as they provide effective protection against malware attacks carried out via externally embedded advertisements.