Adform, a major advertising platform, remained compromised for roughly 24 hours from late on July 26 through the evening of July 27 after being breached by unknown attackers. Few people outside the industry recognize the name, but Adform serves around 1.5 billion ad impressions every day across tens of thousands of websites. That means anyone visiting any site that runs Adform ads could have been targeted. The attackers weren’t trying to install malware. Instead, they ran a script in the victim’s browser that checked the clipboard every three seconds, and if it found a cryptocurrency wallet address had been copied, swapped it for the attackers’ own wallet address. So if someone had a site with the malicious ad open in one browser tab, and was making a crypto transaction in another tab or in a dedicated app, the funds could have ended up in the attackers’ pockets instead. Adform’s owners caught the attack and fixed the problem, but there’s no guarantee a similar incident won’t happen again — which is why every user should defend themselves against malvertising . Check out our tips at the end of this post. What we know about the attack on Adform There isn’t a lot of information out there, since the company’s official statement covers only what happened and when, without getting into the root cause of the incident. Independent research has dug up technical details about how ordinary users were targeted, but none of that explains how Adform itself was breached in the first place. What’s clear is that the attackers slipped their own code into the JavaScript that loaded on every site running Adform ads. Whenever an ad was about to display, the script would load from Adform’s server, pick the right ad, and show it — but the attackers had tacked on a set of malicious functions: monitoring the clipboard, sending data about the site where the encounter happened, and the victim’s IP address back to their own server, and swapping out Bitcoin, Ethereum, and Tron wallet addresses. All it took to make it work was having any site with Adform-served ads open in one browser tab. It didn’t matter what kind of site it was, what the ad looked like, or which advertiser it belonged to. The one thing that mattered was whether the site ran over HTTP or HTTPS. According to Adform, the attack couldn’t succeed on a site loaded over HTTPS since the connection to the attackers’ server was blocked in this case. The company hasn’t shared any information on how many users were affected, or how many sites still serve their content and ads over HTTP. Malicious ads are an everyday occurrence Unfortunately, dangerous online ads have become a systemic problem. And we’re not just talking about sketchy supplement ads or gambling promos — we mean ads that spread malware or lead to sites designed to steal payment details and other valuable data. Attackers have built out industrial-scale infrastructure to pull this off, and they use several different approaches. Hacking and compromising ad servers. Adform isn’t an isolated case: attackers have previously breached Revive ad servers , for one, and spread malware through ads on PornHub . Hijacking the ad accounts of legitimate, reputable brands . All it takes is stealing a password from someone in marketing. From there, the cybercriminals run ads posing as the company they hacked, pushing fake app updates, bogus promotions, and similar scams. In the worst cases — like the account breaches at adtech.de and adxpansion.com — attackers managed to run ads that redirected victims straight into automatic malware installs ( drive-by downloads ). Buying ads directly. That’s right — attackers simply set up their own advertiser accounts and run ads for their phishing sites and malware, just like any other business online. Since ads show up practically everywhere — on websites, in apps, and on social media — these threats can turn up in pretty much any context. And you’ll find variations of this threat on both computers and mobile de…

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