Google has discovered malware misdirecting users of its internet search service.
Google has now taken steps to warn users their computers are infected with the malware.
The malware arrives on victims' desktops as fake antivirus or "scareware" programs. These use misleading warnings about security threats to trick people into purchasing worthless security software, according to security commentator Brian Krebs.
The malware intercepts traffic destined for high-profile domains like google.com, yahoo.com and bing.com. It routes the traffic through intermediate hosts or proxies controlled by the attackers, according to Google security engineer Damian Menscher.
The proxies modify the victim's search results and redirects traffic to pay-per-click schemes that pay for traffic to specific websites.
The malware was discovered after Google engineers noticed some unusual search traffic while performing routine maintenance on one of the company's datacentres.
As a result of the discovery, some people will see a prominent notification at the top of their Google web search results, Damian Menscher said in a blog post.
"We hope that by taking steps to notify users whose traffic is coming through these proxies, we can help them update their antivirus software and remove the infections," Menscher wrote.
Google has published guidelines for search users to scan their own computer systems.