This process of injecting malicious or malware advertisement into legitimate online advertising networks and web pages is called Malvertising.
Some Yahoo Mail users, who were using Google Chrome web browser, may have noticed that Google Chrome blocked access to Yahoo Mail. This is because Google Chrome has a built-in feature called Google Safe Browsing, which is used to block malicious website before you can visit them.
Google Chrome blocking access to Yahoo Mail at mg5.mail.yahoo.com
Now, this malicious advertisement may have appeared on other legitimate websites that serve advertisements from the Eqads.com online advertising networks. So, it is impossible to tell how many computers around the world were infected with malwares because of this malicious advertisement.
As a precautionary measure, we are asking that you use your antivirus software to do a full scan of your computer. Or, you may do a quick antivirus scan with bitdefender.com online virus scanner. Click here to do the quick scan.