Yahoo Mail – How to Prevent Account from Sending Spam

spam-preventionyahoo-mail

My Yahoo email account was sending spam at about 6:40pm today. I immediately updated my password. I also checked "Recent Login Activity", but all recorded locations and IP addresses from 4:47 PM yesterday till now are my own.

How was it possible for my account to send spam while the recorded login activities are normal?

Header of one spam sent and saved in my "Sent" folder:

From Tim Thu Jun 14 15:42:07 2012
X-YMail-OSG: ivy79oIVM1k8kPIPgi4nfJh2JPdWcnzc7If0UmOfBQtmnkB
 nEmfLnPHJ
Received: from [187.41.82.250] by web162602.mail.bf1.yahoo.com via HTTP; Thu, 14 Jun 2012 15:42:07 PDT
X-Mailer: YahooMailWebService/0.8.118.349524
Message-ID: <1339713727.16968.BPMail_high_noncarrier@web162602.mail.bf1.yahoo.com>
Date: Thu, 14 Jun 2012 15:42:07 -0700 (PDT)
From: Tim <tim@yahoo.com>
Subject: HI
To: bankofamerica@replies.em.bankofamerica.com
Bcc: xxx@hotmail.com, xxx@yahoo.com, 
    xxx@gmail.com, 
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Length: 71

Yahoo notice of failure to deliver the spam to some intended address:

Sorry, we were unable to deliver your message to the following address.

<bankofamerica@replies.em.bankofamerica.com>:
Remote host said: 550 5.1.1 <bankofamerica@replies.em.bankofamerica.com> User unknown; rejecting [RCPT_TO]

--- Below this line is a copy of the message.

Received: from [98.139.212.148] by nm21.bullet.mail.bf1.yahoo.com with NNFMP; 14 Jun 2012 22:42:08 -0000
Received: from [98.139.212.214] by tm5.bullet.mail.bf1.yahoo.com with NNFMP; 14 Jun 2012 22:42:08 -0000
Received: from [127.0.0.1] by omp1023.mail.bf1.yahoo.com with NNFMP; 14 Jun 2012 22:42:08 -0000
X-Yahoo-Newman-Property: ymail-3
X-Yahoo-Newman-Id: 395299.5507.bm@omp1023.mail.bf1.yahoo.com
Received: (qmail 91992 invoked by uid 60001); 14 Jun 2012 22:42:08 -0000
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yahoo.com; s=s1024; t=1339713728; bh=3k5IzdOBwo7Jx0VjjcU11ALbzymfvrJ2SheLqHngG7s=; h=X-YMail-OSG:Received:X-Mailer:Message-ID:Date:From:Subject:To:MIME-Version:Content-Type; b=mk5ksTksAaA1u+2GJaaQoJaClM5AQeOmUn4A9e3xYyJVpER/mKvPB6e5NJlZ2WG1zhOvnrMUHGgqwxMMa7lf3K9tHzGxhbLddTxfM0udgCC2Ws4d7ebgACo2lT/92A9qGxxPIXQCSAEiK8/C7P5rQ6ZAOGOv5xMHuSMY3lUzs9Y=
DomainKey-Signature:a=rsa-sha1; q=dns; c=nofws;
  s=s1024; d=yahoo.com;
  h=X-YMail-OSG:Received:X-Mailer:Message-ID:Date:From:Subject:To:MIME-Version:Content-Type;
  b=enSetbkOfQmTtzS221NeSMw+dVAbV6y4iFhhSye/tdOobEqExxBebaFrFsehnXbU10/kB00lr3EVDJFCcYoJT5Sp9a7bz1r9L3CezVCrqeolUUNSN4R9qjreJCxk3YxcTnm9f//PvAIPDsqadFmZyDXcT5FyUEfiwb0cyERbL90=;
X-YMail-OSG: ivy79oIVM1k8kPIPgi4nfJh2JPdWcnzc7If0UmOfBQtmnkB
nEmfLnPHJ
Received: from [187.41.82.250] by web162602.mail.bf1.yahoo.com via HTTP; Thu, 14 Jun 2012 15:42:07 PDT
X-Mailer: YahooMailWebService/0.8.118.349524
Message-ID: <1339713727.16968.BPMail_high_noncarrier@web162602.mail.bf1.yahoo.com>
Date: Thu, 14 Jun 2012 15:42:07 -0700 (PDT)
From: Tim <tim@yahoo.com>
Subject: HI
To: bankofamerica@replies.em.bankofamerica.com
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii

Best Answer

  1. You can have a virus. The one that sends e-mails. If you have at least one spam e-mail try to track computers that had received it in Received header. If it tracks down to your computer - you are vulnerable.
  2. They can just use your e-mail when sending spam. Nothing you can do unless your mail provider (Yahoo) would use something like DKIM or SPF.
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