I am more inclined to believe that your machine has been compromised and your security breached.
Someone got access to your personal Coinbase account and is trying to hack his way in.
Given the situation, I would advise you to change all your current passwords including your email password to secure back your account fully
That's impossible because ... wait for it ... I don't have a Coinbase account and never provided them an email address nor any other vitals. I have never contacted them. I have no issues with Coinbase, it's just that I never had a need for their services. I use BitPay in spite of being critical of them on only one issue stemming from Q3, 2013, but I digress.
I concede that 'bug' may be a better word, with apologies if warranted. I don't have a clue as to how any hacker/bugger obtained one of my obscure email addresses, hence the concern.
No malware detected on my laptop.
Thanks, guys, for the comments, with apologies for the single spelling error that was dulllllly pointed out.
Bruno