Aiming to crack down on a growing problem, Microsoft said it filed five lawsuits Thursday against parties it suspects of posting online advertisements laden with malicious code.
Microsoft has tried to work with ad networks to thwart such "malvertising" in the past, but this is the first time it has gone to court.
"Our filings in King County Superior Court in Seattle outline how we believe the defendants operated, but in general, malvertising works by camouflaging malicious code as harmless online advertisements," Microsoft Associate General Counsel Tim Cranton said in a blog posting.
In each case, Microsoft is suing the unknown parties responsible for the ads.
"Although we don't yet know the names of the specific individuals behind these acts, we are filing these cases to help uncover the people responsible and prevent them from continuing their exploits," Cranton said.
In the past week, The New York Times' Web site was hit with a rogue advertisement that told readers that their computer may be infected with a virus and redirected them to a site that purports to offer antivirus software.
"Scareware is often distributed among criminals, which therefore results in many of the animations a user may see utilizing a common design and interface," a Microsoft told CNET News. "However, without additional information and specific details about the attacks, we cannot be certain that any of today's filings directly relate to the attacks on The New York Times' Web site."
Microsoft likened the latest lawsuits to prior legal action that it has taken against those suspected of click fraud or instant messaging spam.
"This work is vitally important because online advertising helps keep the Internet up and running," Cranton said. "It's the fuel that drives search technologies. It pays for free online services like Windows Live, Facebook, Yahoo, and MSN. Fraud and malicious abuse of online ad platforms are therefore a serious threat to the industry and for all consumers and businesses that rely on these free services."