If you see a notification above your Google search results that your computer is infected with malware, it's probably best to take it seriously - the search giant has identified traffic patterns consistent with infection, and it's letting users know that they need to take action.
The malware in question routes Google traffic through a small number of proxies, according to the official blog entry. If Google's search engine detects that you're coming to them through these intermediaries, it'll display a banner notification (pictured right) in hopes that you'll fix the problem.
They're even providing those affected with tutorials on how to update antivirus software to scrub the computer of this strain of malware, which makes sense given that infection rates are very likely higher amongst the technology-illiterate.
Google discovered the infections when some unusual search data was turned up by a routine maintenance cycle. This particular infection was singled out as the culprit after Google shared that data with outside security professionals from the companies that were sending the modified search traffic.