Malicious Advertisements (malvertising)

Malicious ads (also known as “malvertising”) may also be a way for a website to experience a malware attack. Rather than infecting a website directly, the hackers infect an ad network (perhaps even by simply creating an ad that looks legitimate, but actually serves malware to the user). One their malicious ad is in the ad network, it can be presented to users on various websites by the ad network simply rotating through its inventory of ads. This is often a difficult attack to detect on a website.

Example of a malvertising popup imitating anti-virus software

The reason is that the malicious code may show up intermittently on various user requests, and unless you happen to observe the malicious ad being served, you will not be able to detect the malicious code on the website.

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