Yahoo.com Malware Attack

[Corrine]

Thousands of visitors to yahoo.com hit with malware attack, researchers say

Two Internet security firms have reported that Yahoo's advertising servers have been distributing malware to hundreds of thousands of users over the last few days. The attack appears to be the work of malicious parties who have hijacked Yahoo's advertising network for their own ends.

According to Yahoo, they identified an ad designed to spread malwareand "immediately" removed it. I'm not so sure how "immediately" it was since the report indicates it started December 30.