In reply to a post by bobble_bob:

went into my Yahoo account and got a few "delivery failed" messages which were the email addresses copied in that are probably no longer active.

This happened to my account. Someone in Croatia hacked in and used it to send spam.

What (if anything) can I do about it? Would changing the password stop it from happening again?

Yes, it should do, but check ALL your account settings to make sure they have not been compromised.

Nothing of mine had changed, but it does seem everyone who has been compromised had their account accessed from Bulgaria or Turkey using Yahoo Mobile

Some people who changed their passwords are saying they're locked out of their accounts. So maybe it's a bad idea to change the password?

This happened to 2 of my yahoo accounts also (i have 3 in total). I've not clicked on any spam link. I scanned my pc will full scan setting with both Avast and malwarebytes and both came up clean.

In my situation they seemed to spam email and CC me a copy too. As someone else stated they seem to spam a few email addresses. Some are valid friends emails and some seem to be made-up.

I changed my passwords on both accounts. Nothing since, though unfortunately some of my friends who were on spam list, tried to spam me back.

The commonality of all this does suggest that the yahoo mailing system is the common de-nominator. I suspect that they were compromised on a big scale and instead of telling people, admitting they were at fault, they have kept their head down since nothing happened immediately. Now it seems it as.

Hope they fix it soon. Change password if you can.

Does seem as though Yahoo is the weak link, I've read there was a major breach in New Zealand last month. Here in the UK the BT Community forums have had 250 posts in one week http://community.bt.com/t5/Other-BB-Queries/BT-email...

And BT Yahoo, if you can get them seem to be saying it's the customer's fault. Their silence is deafening.

Yahoo have come out now and admitted some of their accounts were compromised. The guy who works for BT who posts on that forum you linked so said so.

Me and a few others have now started getting silent calls and spam calls from international numbers that started a day or so after being hacked. Funny that!

I just followed these instructions http://help.yahoo.com/kb/index?locale=en_US&y=PROD_A... to see the recent yahoo login activity of the email account and on mine someone from poland logged in on march 5th. At first via Yahoo! Mobile and then via the browser at 20:12. I logged back in 12 minutes after he did. It's worth a look though. I wish the history went back further though. I'm sure my 2nd email was compromised too but it only goes back to when I logged back in. So I cant see the offending hackers details.

Anyone who's been hacked, tweet Channel 4 News

https://twitter.com/geoffwhite247

http://www.channel4.com/news/yahoos-email-system-hac...

So do we know how they did it?