Join The Community!
I'm not sure what to make of your problem. Someone once told me I was spamming them. Checked my computer didn't find anything. I never heard anything back from anyone else so I dropped it.
But my IT friend recently recommended this free anti virus for Mac.
I just re-read your post title and deleted my initial response. Make sure the SPAM email they are getting is not infected with anything more dangerous, then as a few of your contacts to forward these emails to you. The message should contain data that shows the internet path it took to get to them and perhaps is you can actually trace it back to your IP address. Typically, this is a Trojan Horse that looks at your contact list and sends the email. But, since it's a Yahoo account, I don't know where they are looking. Have you used any of the services that connect your contact list to other services, like Facebook? Do you maintain a a local copy of your contacts that you sync with your computer?
You may want to write Yahoo and see what they have to say, there may even by info on their site regarding email Spam. And you should also do a complete virus and malware scan of your computer - I'm STILL a PC user, so I don't know of a good Mac program for this.
It could be that this message that people are getting is not actually from your mail account. Like Lon says, when a friend tells you they got a msg from you, that email should have everything to track the source to confirm it is not coming from you.
I can send an email to anyone and make it "appear" to be be from you Murray.
If I had access to your Yahoo Account for only 10 minutes, I could easily get a list of every person you've every sent an email to and everyone you have ever received an email from. Not only that, but I could also get a list of everyone on your contact list.
Then, if you change your Yahoo Password, it wouldn't matter. I could just send emails that "appear" to be from your email address and it would be just as effective as if I actually sent them from your account, providing I simply send them to the people that I extracted from your account.
Does that make sense?
If they lifted your contact list, I cannot think of anything you can do. I wonder if anyone else has suggestions.
If that is the case, should be okay for now. Keep those passwords strong. :)