Best answer as chosen by user horningseatakalamakan: I don't think there is a problem here at all
You do not have a hacking problem. What you see there is a result of someone who has your email address on their computer and that computer has a virus. (or is part of a bot-net)
The virus has its own email engine, which makes it independent of the users own mail carrier, and goes around the infected PC looking for email addresses. They are all over the place on a computer. It collects them all up, composes an email, sometimes a replica of the virus and sometimes just Spam, and selects one of the addresses that it found as the From address.
In your case, you were the lucky contestant. Obviously not all the email addresses were valid which triggers the far end email server to send an "unable to deliver" message to the Sender. As your address was chosen as the From address, guess who gets the bounce messages.
Bottom line, No Hacker.
The toolbar "problem". Reboot the Mac and go back into Mail. Now try Customizing the toolbar again. Dragging any of the icons off the toolbar and into the Customize window will cause that icon to vanish in a 'poof"
Relax, no problems.
By the way, did know that there is a whole set of Mac forums here on CNET where you will get a much faster response to any Mac problems that you have.
You will find them at http://forums.cnet.com/mac-forums/?tag=TOCleftColumn.0;blankArea.5
See you over there