Google announced today that some users will see a message at the top of their search results telling them that their computer is infected, after the company discovered some unusual search activity.

“As we work to protect our users and their information, we sometimes discover unusual patterns of activity,” explains security engineer Damian Menscher. “Recently, we found some unusual search traffic while performing routine maintenance on one of our data centers. After collaborating with security engineers at several companies that were sending this modified traffic, we determined that the computers exhibiting this behavior were infected with a particular strain of malicious software, or ‘malware.'”

“This particular malware causes infected computers to send traffic to Google through a small number of intermediary servers called ‘proxies,'” says Menscher. 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.”

Matt Cutts said on Google+, “We’re trying this as an experiment to alert and protect consumers that we believe have infected machines. Please share this widely…This is malware that’s specific to Windows. Remember to do an actual search (any search will do) and check the top of the search results page; don’t just go to the home page.”

Menscher brings up the possibility that the message might not actually reach everyone, but offers users an alternative way to see if their computer is infected. He points to a three step process here.

Google offers additional security advice here.