Most of the Yahoo Email Id has been under hack. Sending some Automated URL's through mail to your contacts list, unfortunately you couldn't see those mails in sent items. Yahoo maintaining silence in this issue. If you get any reply from your real friends ask them regarding this issue.
Action Required:
If you experience this Send an email to all your friends regarding this issue through email or Facebook.
Change your password take a backup of your contacts in CSV format delete your contacts from Yahoo mail for some days. Some of my friends has been attacked by this virus. I attached the picture which I took from my mail.
I received two email's from two friends within the time gap of 20 minutes. I think it spreading vigorously.  

 I clicked the link above which is in pic. My AVG showing the threat has been detected, virus named as EXPLOIT ROGUE Scanner. I think this attack has been originated from Russia because after clicking the above url it has been redirected to (Don't click this) ru is a Russian TLD(Top level domain). So be safe with this URL.

If you are without antivirus or updated antivirus surely all the passwords stored in your PC mailed to hacker. Then your mail, credit card, netbanking passwords all would be compromised by the hacker.

 Make sure don't enclose your personal data in any of the email it may be a Phishing attack. Be safe make your browsing safe