My Mac Email is sending out random emails

Question

When I set up my computer, I attached my yahoo email with my mail app. Periodically my daughter will receive strange emails from me and the body of the message is whatever website I have been browsing. From my email (yahoo) inbox, to facebook, random websites, etc. For the longest time we just thought it was spam and changed passwords but it is still doing it. Today, my daughter opened the mail app and discovered all those old sent messages in the mail app sent box. What in the world is going on??? I deleted my yahoo email account from the mail app just today. Scary stuff! I want to know why this is happening. Every now and then when I log on to my computer, that mail icon jumps up and down and requests a password. Now I know, its probably associated with the strange emails being sent out...which I am not doing by choice. I just want it to go away! The pages that are being sent (facebook, yahoo inbox) are live pages with active links....it's crazy.

Answer 1

Please read this whole message before doing anything.
This procedure is a diagnostic test. It won’t solve your problem. Don’t be disappointed when you find that nothing has changed after you complete it.
Third-party system modifications are a common cause of usability problems. By a “system modification,” I mean software that affects the operation of other software — potentially for the worse. The following procedure will help identify which such modifications you've installed. Don’t be alarmed by the complexity of these instructions — they’re easy to carry out and won’t change anything on your Mac. 
These steps are to be taken while booted in “normal” mode, not in safe mode. If you’re now running in safe mode, reboot as usual before continuing. 
Below are instructions to enter some UNIX shell commands. The commands are harmless, but they must be entered exactly as given in order to work. If you have doubts about the safety of the procedure suggested here, search this site for other discussions in which it’s been followed without any report of ill effects. 
Some of the commands will line-wrap or scroll in your browser, but each one is really just a single line, all of which must be selected. You can accomplish this easily by triple-clicking anywhere in the line. The whole line will highlight, and you can then copy it. The headings “Step 1” and so on are not part of the commands. 
Note: If you have more than one user account, Step 2 must be taken as an administrator. Ordinarily that would be the user created automatically when you booted the system for the first time. The other steps should be taken as the user who has the problem, if different. Most personal Macs have only one user, and in that case this paragraph doesn’t apply. 
Launch the Terminal application in any of the following ways: 
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.) 
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens. 
☞ Open LaunchPad. Click Utilities, then Terminal in the icon grid. 
When you launch Terminal, a text window will open with a line already in it, ending either in a dollar sign (“$”) or a percent sign (“%”). If you get the percent sign, enter “sh” and press return. You should then get a new line ending in a dollar sign. 
Step 1 
Triple-click the line of text below to select it:
kextstat -kl | awk '!/com\.apple/{printf "%s %s\n", $6, $7}' 
Copy the selected text to the Clipboard by pressing the key combination command-C. Then click anywhere in the Terminal window and paste (command-V). Post the lines of output (if any) that appear below what you just entered. You can do that by copying and pasting as well. Omit the final line ending in “$”. No typing is involved in this step.
Step 2 
Repeat with this line:
sudo launchctl list | sed 1d | awk '!/0x|com\.(apple|openssh|vix)|edu\.mit|org\.(amavis|apache|cups|isc|ntp|postfix|x)/{print $3}' 
This time you'll be prompted for your login password, which you do have to type. It won't be displayed when you type it. Type it carefully and then press return. You may get a one-time warning to be careful. Heed that warning, but don't post it. If you see a message that your username "is not in the sudoers file," then you're not logged in as an administrator. 
Note: If you don’t have a login password, you’ll need to set one before taking this step. If that’s not possible, skip to the next step. 
Step 3
launchctl list | sed 1d | awk '!/0x|com\.apple|edu\.mit|org\.(x|openbsd)/{print $3}' 
Step 4
ls -1A /e*/mach* {,/}L*/{Ad,Compon,Ex,Fram,In,Keyb,La,Mail/Bu,P*P,Priv,Qu,Scripti,Servi,Spo,Sta}* L*/Fonts 2> /dev/null  
Important: If you formerly synchronized with a MobileMe account, your me.com email address may appear in the output of the above command. If so, anonymize it before posting. 
Step 5
osascript -e 'tell application "System Events" to get name of every login item' 2> /dev/null 
Remember, steps 1-5 are all copy-and-paste — no typing, except your password. Also remember to post the output. 
You can then quit Terminal.