Visitors to Yahoo.com over the past week may have been affected by malware coming from the siteâ€™s ads.
According to online security firm Fox IT based in the Netherlands, users who clicked on ads from the site were redirected to sites that exploited vulnerabilities in Java and installed a host of different malware.
â€˜Clients visiting yahoo.com received advertisements served by ads.yahoo.com,â€™ the internet security firm posted on its blog. â€˜Some of the advertisements are malicious.â€™
Fox IT estimates tens of thousands of users were affected per hour.
â€˜Given a typical infection rate of 9%, this would result in around 27,000 infections every hour,â€™ the company said.
â€˜Based on the same sample, the countries most affected by the exploit kit are Romania, Great Britain and France. At this time itâ€™s unclear why those countries are most affected, it is likely due to the configuration of the malicious advertisements on Yahoo.â€™
Yahoo has issued a statement about the security breach:
â€˜At Yahoo, we take the safety and privacy of our users seriously,â€™ it said in a statement Saturday night.
Fox IT was unable to identify those responsible for the attack but says it was â€˜clearly financially motivated.â€™
The firm provides details on how to prevent the malware accessing your computer by blocking IP addresses of the malicious ads and the exploit kit.
Computers connected to a network can spread the malware onto many more computers.
The malware may have begun spreading from December 30.
Yahoo says it is monitoring the problem.
â€˜We recently identified an ad designed to spread malware to some of our users. We immediately removed it and will continue to monitor and block any ads being used for this activity.â€™
Millions of visitors to Yahoo.com hit by malware attack