More generally make sure you keep your antivirus definitions up to date
MalwareBytes is a good additional program too. Download the free version and run it manually now and then. Being manual it doesn’t conflict with your antivirus but does find and delete Malware and Adware programmes which often arrive in dodgy emails and sit on your computer waiting to do mischief.
I wonder what the connection is? I have had them from (not) David Watson & (not) Mark Daniels.
They don't get far but they do get about.
I think it's done by hacking into people's e-mail address books, then sending e-mails to these addresses that look as if they've come from other addresses in the same address book. Chances are that two people who appear in the same address book will also know each other and could be fooled into thinking the e-mail is genuine.