According to Twitter users, sites such as The New York Times, The Huffington Post, Los Angeles Times, Washington Post and many others were being blocked by Google's Chrome browser with warnings about possible malware -- malicious software that could infect a user's computer -- emanating from ad company Netseer.
"Content from cm.netseer.com, a known malware distributor, has been inserted into this Web page. Visiting this page now is very likely to infect your computer with malware," a Chrome message said Monday morning when a user attempted to visit the San Jose Mercury News' website.
Netseer, a Santa Clara, Calif.-based startup founded in 2006 that helps target ads based on website content, suffered a hacking attack on its website but said Monday that it was not actively issuing malware-infected ads.
"This morning at approximately 5:30 a.m. Pacific time, our third-party hosted corporate website (netseer.com) was hacked and infected with malware. Consequently, Google added our domain to the list of malware affected website. Our operations team went into all-hands-on-deck mode, and we have successfully cleaned the site of the malware issue," spokeswoman Kathleen Formidoni said.
Because the company's corporate site and ad-serving infrastructure share the same domain, the block Google served to keep malware placed on Netseer's website from spreading also affected ads Netseer placed on other sites. But "the malware was never served into ad serving stream," Formidoni wrote in an email.
In an email response to a request for comment, a Google spokeswoman said the company does not comment on individual malware cases.
Bob Mason, chief technology officer for Mercury News parent Digital First Media, said MercuryNews.com and the company's other websites are not infected with malware, but the company is taking steps to make sure any virus is blocked from its websites.
Other news sites have taken to Twitter to ensure readers that their content does not include any malicious code.
"Hello, Chrome users. We're aware some of you are seeing malware warnings about Guardian articles. Please ignore; no risk," GuardianTech, the Twitter account for The Guardian's technology news, wrote Monday morning.