What happened: "The ads were served in iframes by Yahoo's advertising service, and were hosted on external sites. Upon clicking the advertisements, users would be redirected to a selection of other domains, all reporting the same Netherlands-based IP address.
The malware users were faced with include money-grabbing Zeus Trojan, botnet software Andromeda and other malware associated with advertising."
Yahoo found serving Java malware-spreading ads
Security issues sees thousands of web users at risk