NEW YORK (CNNMoney) -- Google said Wednesday that it has begun to display a malware warning in its search results to a group of users with infected computers.
The search company said it discovered a certain strain of malware when performing maintenance on one of its data centers. Google (GOOG, Fortune 500) noticed some "unusual search traffic" coming from some computers that were sending requests to Google through a small number of intermediary servers called "proxies."
The infected computers included those from several companies, whose security engineers helped Google analyze the traffic. They determined that the computers that were rerouting traffic through the proxies were infected with the same malicious code.
Users whose computers are sending requests to Google through those proxies will now see a big yellow notification at the top of their search results that indicates their PC may be infected.
"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," said Damian Menscher, security engineer at Google, in a blog post.
Google's notification only applies to those whose computers are infected with the particular strain of malware that it discovered. Google didn't give any details about what the malware that they discovered does, other than saying attackers can control compromised computers' Internet traffic.
Some malware allows attackers to gain full control of a computer or log key entries to steal users' credit card numbers or credentials like usernames and passwords.
Malware can be inadvertently installed by a user by clicking on an infected e-mail attachment or downloading a compromised advertisement on a website.
Google's notification links to a Q&A about how to resolve the infection, including a list of reputable antivirus programs. 
