Although it might sound a little bit incredible that a super giant like Yahoo can be affected by this kind of problem, it seems like the Sunnyvale company distributed a malicious advert which attempted to infect users' computers. What's more interesting is that the ad was distributed by Right Media, the company which recently became 100 percent owned by Yahoo after the Sunnyvale giant acquired the remaining shares for $650 million. According to The Register, the infected ad was placed on very popular Internet websites such as MySpace, PhotoBucket and Bebo but there is no official number of potential infected users. However, the banner was displayed for no less than 12 million times so some of the visitors might be still infected.

In case you don't know for sure whether you're infected or not, you should know that the Trojan file distributed by the advert is actually the Downloader.VBS.Agent.n which can only affected the systems without the Microsoft Security Bulletin MS07-009. This Microsoft security patch was rolled out on February 13, 2007 so, if you have the Windows AutoUpdate feature enabled, there's no reason to get worried.

"The ad has been identified as a high risk creative and banned from the exchange. However, we cannot control what happens elsewhere on the Net. We continue to enhance our protective tools and are committed to finding ways of keeping this type of activity away from consumers and publishers," a Yahoo representative said for The Register.

Obviously, there is not much to do in order to remain protected. However, you're advised to patch your operating system with the latest updates rolled out by Microsoft as well as your antivirus product with the newest virus definitions. Although Yahoo might already fixed the issue, you can always get infected by visiting a dangerous page 'equipped' with this kind of threat.