possible worm

I think a acquired a worm in my iMAC after trying to open what I thought was a  FEDEX email. The reason I think I have a worm is that a few days after this email I had a phony charge on one of my credit cards. Of note, the day before the phony charge I had scheduled a payment for this credit card.

 

I have installed the Mac edition of 'Internet Security.'  The program has scanned my computer and has found no virus and the phishing websites are blocked now.

 

The question I have is this...Do I still have to worry about this potential worm?  And if so, what do I need to do next?