Recently I received CCs from two women i've met, each eMail was spam for a concentrate seen on the Dr OZ show?
One woman let me know when I eMailed back that there are warnings about the company selling this product. She indicated she had NOT sent the CC, her eMail had been "HACKED". After I found warnings about this product I eMailed the first sender a note that when she CCs something it contains the eMail infor for every one in the CC?! That CCing anyone winds up notifying everyone about the other people in her list which has the potential of disseminating information that might cause problems? Plus, a recepient might have information to cause problems for the woman? Unfortunately, I didn't receive a reply from her letting me know her eMail was hacked. I regularly delete all sent eMail, delete read eMail from women I've met, delete theeir phone numbers from my cell unless I've altered the number so that what is seen is NOT their number, remove tracks that lead to where their incall is from my GPS. Any information left in my computer is coded. I "clean" my cell and GPS incase I loose them. or they are stolen. Plus if for some reason I'm either detained or arrested by authorities there isn't any information leading to anyone. My chances or being detained or arrested should be extreemly low, hasn't happened to me since the mid 70s, but, if it happens, or I'm in a serious or deadly accident, there isn't trail to anyone. I've got all of the parts to build another computer--it's main operating system will NOT be Windows, but rather Ubuntu, a free operating system that is easy to master for simple tasks such as internet, eMail, downloading, word processing etc. Deprived and discreteI get spam emails from guys all the time. I simply delete and advise them of the situation, while suggesting they change their password. It's only harmful if some devious person decides to take note of the names/emails of the other recipients. Or if one of the recipients you know from "real life" decides to google the other recipients, and puts 2 and 2 together.
I just realized that, aside from deleting all of your email accounts, there really is no solution to this problem. It's a hazard of our hobby-world that we deem worth the risk. But if you're getting the side-eye from Betsy at work, it is because she somehow got CCd some spam from you; and saw bigbustyblonde, xxxHotChicksxxx, and CumHere in the recipient list lol
I would be more concerned about this if I showed my face in my ads or website. Fortunately, I don't 
But for the guys I can see how this is (could potentially be) a big issue, when hackers can grab contacts from both your work/personal email and hobby email, and CC ALL of them. And, the names you guys use for your hobby emails are inconspicuous. They don't scream debauchery, like ours do lol
Just because you received an email that says it was from someone doesn't mean it was. I don't mean it could have been from someone else using their account, I mean you can make your email appear to say it was sent from ANY email address on casual glance. It is actually a common tool for spammers to forge the sender address to both hide who may actually be hacked (if anyone) and also to make your email appear it may be from someone you know and thus make it more likely that you would open it.
In the case you mentioned it is possible that no one had their email hacked. Or that someone just has a virus and the virus is sending out spam. When it does it it will use their address book and send out to those in the address book pretending to be someone else int he address book. This actually sounds a bit like what you received.
So rather then worry about being hacked (though it can happen) people usually need to just be more careful about malware and viruses. Downloading malwarebytes and doing a scan is a good start and the $25 full version fee is worth it. Don't keep client info in your email contacts. Ever.
In regards to security, the best practice is not to change your password often. In fact that doesn't provide you with any more security then just using a secure password in the first place. The best thing is to use a service that supports 2 factor authentication (which gmail does).