Millions of people visiting weather.com, drudgereport.com, wunderground.com, and other popular websites were exposed to attacks that can surreptitiously hijack their computers, thanks to maliciously manipulated ads that exploit vulnerabilities in Adobe Flash and other browsing software, researchers said.

The malvertising campaign worked by inserting malicious code into ads distributed by AdSpirit.de, a network that delivers ads to Drudge, Wunderground, and other third-party websites, according to a post published Thursday by researchers from security firm Malwarebytes. The ads, in turn, exploited security vulnerabilities in widely used browsers and browser plugins that install malware on end-user computers. The criminals behind the campaign previously carried out a similar attack on Yahoo’s ad network, exposing millions more people to the same drive-by attacks.

Update: A few hours after Ars published this article, Malwarebytes updated the blog post to say the campaign had moved to yet another ad network, which happens to be associated with AOL. Visitors to eBay were among those who were exposed to the malicious ads distributed through the newly discovered network.