As many as two million computers could be infected with new malware that Google is alerting visitors to on its search pages, with hundreds of thousands already warned that they may be infected.
Google security engineer Damian Menscher explained in an updated blog post that the malware is thought to have infected computers via "one of roughly 100 variants" of fake anti-virus software.
"We aren't aware of a common name for the malware," he added.
Menscher had said in the original post that Google would flash up a warning message if a user coming to its search page appeared to do so "through a small number of intermediary servers called proxies", indicating that they were infected.
"We hope that by taking steps to notify users whose traffic is coming through these proxies, we can help them update their anti-virus software and remove the infections," he said.
However, some have complained that the warning notice could be spoofed by hackers hoping to trick them into visiting a dangerous site instead of the help page to which it links.
"We thought about this, too, which is why the notice appears only at the top of our search results page. Falsifying the message on this page would require prior compromise of that computer, so the notice is not a risk to additional users," Menscher explained.
"In the meantime, we've been able to successfully warn hundreds of thousands of users that their computer is infected. These are people who otherwise may never have known."
Cotton seedling freezes to death as Chang'e-4 shuts down for the Moon's 14-day lunar night
Fortnite easily out-earns PUBG, Assassin's Creed Odyssey and Red Dead Redemption 2 in 2018
Meteor showers as a service will be visible for about 100 kilometres in all directions
Saturn's rings only formed in the past 100 million years, suggests analysis of Cassini space probe data
New findings contradict conventional belief that Saturn's rings were formed along with the planet about 4.5 billion years ago