Between 300,000 and one million PCs have been affected.
Microsoft's digital crimes unit and Symantec have taken down a Bamital botnet which hijacked online search results without the knowledge of users.
After being attacked with the botnet, the infected PCs failed to search the web.
The botnet installed malware onto user computers, stole personal information, and fraudulently chargde businesses for online advertisement clicks.
Microsoft Digital Crimes Unit assistant general counsel, Richard Domigues Boscovich, said that the Bamital botnet defrauded the entire online advertising platform, which is what allows the Internet and many online services to be free.
"What's most concerning is that these cybercriminals made people go to sites that they never intended to go, and took control of the computer away from its owner," Boscovich said.
"Because this threat exploited the search and online advertising platform to harm innocent people, Microsoft and Symantec chose to take action against the Bamital botnet to help protect people and advance cloud security for everyone."
Over the last two years there were about eight million computers attacked by Bamital, in addition to search hijacking and click fraud schemes the research by Microsoft and Symantec revealed.
"Microsoft is also using the intelligence gathered in this operation to work with Internet service providers and Computer Emergency Response Teams to help victims regain control of their computers," Boscovich said.
"We've found that cleanup efforts like this not only help clean people's computers, but they also take the very infrastructure the botnet needs to be impactful and profitable away from the cybercriminals."