Google has dusted off a  tool it last used nearly a year ago to warn users infected with the "DNSChanger" malware. Special messages are being displayed at the top of a Google search results page to people whose Windows PCs and Macs have been infected with malicious code that hijacks their computer.

Damian Menscher, a Google security engineer, in a post to a company blog said the goal with this notification is to raise awareness of the DNSChanger malware among affected users.

"We believe directly messaging affected users on a trusted site and in their preferred language will produce the best possible results," he said.

DNSChanger silently redirects clicks by modifying victimized computers' domain name system (DNS) settings. The users are sent to hacker-created websites that resemble the real domains. The servers were taken over by the FBI which administered them for a while to give users the chance to remove the software from their computers.

However the court has ordered the servers are switched off which means that 100,000 people are expected to lose their internet connection.