A group of hackers took advantage of Yahoo’s popular network of sites to perpetrate a wide-spread attack on visitors to those sites through ads. The aim was to get malware onto users’ computers and take advantage of outdated versions of Flash running on their machines.
The malicious advertising (“malvertising”) campaign began on July 28, according to online security software firm Malwarebytes, which detected the activity. The New York Times reports that the hackers bought ads across the Yahoo network. When users on Windows machines visited those sites, the malicious ads could automatically download malware onto unprotected computers. The malware then searched for an outdated version of Adobe Flash through which it could take over the computer and either demand ransom from the user to get control back or generate revenue for the hackers by driving Web traffic to websites that pay them for visits.
A Yahoo spokesperson said of the attack, “As soon as we learned of this issue, our team took action and will continue to investigate this issue. Unfortunately, disruptive ad behavior affects the entire tech industry. Yahoo has a long history of engagement on this issue and is committed to working with our peers to create a secure advertising experience. We’ll continue to ensure the quality and safety of our ads through our automated testing and through the SafeFrame working group, which seeks to protect consumers and publishers from the potential security risks inherent in the online ad ecosystem.”
The campaign ran for about a week, according to Malwarebytes. Yahoo was able to stop the activity and remove the malware from the network soon after the security firm notified it.
It’s not clear how many users were affected by the campaign, but a Yahoo spokesperson told the Times that the “scale of the attack was grossly misrepresented in initial media reports, and we continue to investigate the issue.”
Exploiting Adobe Flash is not new, and continued vulnerabilities recently led Mozilla, Facebook and others to call for its end. Adobe is urging users to keep their versions of Flash up-to-date for “the latest security updates.”