Today, many websites earn revenue by displaying online advertising on their websites. And, attackers are taking advantage of that to spread malware using malvertising. What is malvertising? How do attackers use this to spread malware, and how can we prevent it? Let’s understand that in more detail.

What is malvertising?

When a website displays ads on its web pages, the contents of the ads are decided by some third-party ad networks. The ad contents keep changing. So, if one of the ad contents is malware, it becomes very difficult for the website or the users to detect. When one such ad content shown on a web page is malicious, and a user visits the web page, then the user’s computer can get infected by the malware.

In malvertising, attackers inject malware-laden online advertisements into legitimate online advertising networks. Those ads are displayed on legitimate websites. As the websites on which the malvertisements are displayed are legitimate ones, the malware can infect a huge number of users before the malvertisements get detected.

Malvertising is a fairly new concept for spreading malware. Usually, they can bypass firewalls and they can use drive-by download (What is a drive-by download?), in which a user does not need to click on a link to initiate a download.

How does malvertising work?

Malvertisements can infect a computer pre-click or post-click.

A pre-click malvertisement can be embedded in the main scripts of the page. They can even initiate drive-by-download on visiting the malvertising-laden website. A drive-by-download (What is a drive-by download ?) is a download in which a user does not need to click on any link and initiate the download. When a user visits the webpage, the malware starts downloading automatically in the background.

For a post-click malvertisement, it infects a computer when a user clicks on the ad to see the advertisement. The user is redirected to a malware-infected website.

The first recorded malvertisement was reported in late 2007 or early 2008. It exploited a security vulnerability of Adobe Flash and affected a number of platforms, including MySpace, Excite, and Rhapsody. Since then, malvertising has continued unabated and affected many computers.

How to prevent malvertising?

We can protect ourselves from malvertisements in the following way: