Spoof/Spam emails on Mac

I started getting the bounced emails from "my" email account a couple of months ago--on my Mac. Now, I'm no longer getting bounced emails, but I am getting a load of emails sent TO my (real) account, FROM "my" (hijacked) email account. Most are advertising "enhancement/enlargement" products, but some are for Rx meds and other garbage.
Does anyone know if my email account was easier to hijack because I use Microsoft Entourage? If I'd used a mac.com email address, would this not have been a problem?
Thanks for any input/advice,
Pam

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