Q: My email was hacked and used to send Spam. Do I need to run a virus check or just change password?

Do not install or run an anti virus app.

How do you know your email was "hacked"? It is a common practice for spammers to spoof any sent from email address. It may be that your email address was spoofed. There is nothing for you to do if this is the case. The spammer will soon move on and spoof another email address.

It is a good idea to immediately change your email password if indeed someone has gained access to your email account.

No. Almost a 100% certainty they hacked into your account at your ISP. Change the password to something much more difficult to crack or guess.

You also may not have been hacked at all. Spammers randomly use email addresses to send out thousands of junk emails by spoofing the sender name. They didn't come from you in any way, even though your name is listed as the sender.

I received a couple hundred returned emails over the past 2 days that my provider caught as spam and didn't deliver.

Yup, a clear sign that either your address was simply being spoofed, or a hacker got into your email account at your ISP. Had they come directly from your Mac, you'd have hundreds of sent emails in your outbox.

What happens with these returns is that the spammers just blindly send out thousands of emails, such as to a@geronimo.com, b@geronimo.com, etc. Those that exist go through. The once that don't get bounced by the receiving email server as undeliverable. Because your address was used or spoofed as the sender, the bounce messages come to you.