Malvertisement - malware advertisement - is an infected online advertisement. These ads may be hosted in malicious as well as legitimate sites, and social networks. If a user clicks on a malvertisement, the user's system becomes infected with a malware. The use of infected ads allow cybercriminals to spread malware easily.
By targeting flaws in the delivery of ads such as flaws in third party ad servers or flaws in redirection of ads to legitimate sites, cybercriminals are able to spread malware and/or redirect users to malicious websites.