Malvertising

Malvertising, a portmanteau of malicious software and advertising, is the use of online advertising to spread malware, typically by injecting malicious or malware-laden advertisements into legitimate online advertising networks and webpages. Because advertising content can be inserted into high-profile, reputable websites, the technique lets attackers reach users who might otherwise avoid or be protected from their attacks by firewalls or other safety precautions, and it can be spread across a large number of legitimate websites without directly compromising any of those websites themselves. Infections delivered through malvertising typically require no action from the user, such as clicking, and exploit no vulnerability in the website or server hosting the advertisement; the malicious code instead travels silently through the advertisement itself. The technique has grown rapidly and is difficult to combat: in 2012, an estimated nearly ten billion ad impressions were compromised by malvertising, and companies and websites have had difficulty reducing the number of malvertising attacks.