malvertising

thumb|An example of a malicious advertisement, claiming that the computer is infected Malvertising (a portmanteau of "malicious software (malware) advertising") is the use of online advertising to spread malware. It typically involves injecting malicious or malware-laden advertisements into legitimate online advertising networks and webpages. Because advertising content can be inserted into high-profile and reputable websites, malvertising provides malefactors an opportunity to push their attacks to web users who might not otherwise see the ads, due to firewalls, more safety precautions, or the like. Malvertising has been described as "attractive to attackers because it 'can be easily spread across a large number of legitimate websites without directly compromising those websites'."

Malvertising can be extremely hard to combat because it can quietly work its way into a webpage or webpage advertisement and spread unknowingly: "The interesting thing about infections delivered through malvertising is that it does not require any user action (like clicking) to compromise the system and it does not exploit any vulnerabilities on the website or the server it is hosted from... infections delivered through malvertising silently travel through Web page advertisements." It is able to expose millions of users to malware, even the most cautious, and is growing rapidly: "In 2012, it was estimated nearly 10 billion ad impressions were compromised by malvertising." Attackers have a very wide reach and are able to deliver these attacks easily through advertisement networks. Companies and websites have had difficulty diminishing the number of malvertising attacks, which "suggests that this attack vector isn't likely to disappear soon."